U.S. patent number 7,106,544 [Application Number 10/840,857] was granted by the patent office on 2006-09-12 for servo systems, servo heads, servo patterns for data storage especially for reading, writing, and recording in magnetic recording tape.
This patent grant is currently assigned to Advanced Research Corporation. Invention is credited to Matthew P. Dugas, Theodore A. Schwarz, Gregory L. Wagner.
United States Patent |
7,106,544 |
Dugas , et al. |
September 12, 2006 |
Servo systems, servo heads, servo patterns for data storage
especially for reading, writing, and recording in magnetic
recording tape
Abstract
Methods and systems for data recording and reading for
increasing overall tape data storage density, especially for data
written in azimuth style. The principles of the invention provide
servo formats and systems that allow accurate on track guidance for
higher density applications and that are less sensitive to off
track error. Preferred embodiments of the invention offer servo
formats and systems of the invention that allows positive track and
group identification at the beginning, end, and optionally
periodically along the length of a tape.
Inventors: |
Dugas; Matthew P. (St. Paul,
MN), Schwarz; Theodore A. (St. Paul, MN), Wagner; Gregory
L. (Arden Hills, MN) |
Assignee: |
Advanced Research Corporation
(Minneapolis, MN)
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Family
ID: |
33458761 |
Appl.
No.: |
10/840,857 |
Filed: |
May 7, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040223248 A1 |
Nov 11, 2004 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60509031 |
Oct 6, 2003 |
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60469519 |
May 9, 2003 |
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60469517 |
May 9, 2003 |
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Current U.S.
Class: |
360/75; 360/121;
G9B/5.005; G9B/5.075; G9B/5.203 |
Current CPC
Class: |
G11B
5/00813 (20130101); G11B 5/29 (20130101); G11B
5/584 (20130101); Y10T 29/49128 (20150115); Y10T
29/49032 (20150115); Y10T 29/49044 (20150115); Y10T
29/49046 (20150115); Y10T 29/4906 (20150115); Y10T
29/49052 (20150115); Y10T 29/49043 (20150115); Y10T
29/49048 (20150115) |
Current International
Class: |
G11B
21/02 (20060101) |
Field of
Search: |
;360/75,77,12,48,119,121
;29/603.13 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wong; K.
Attorney, Agent or Firm: Kagan Binder, PLLC
Parent Case Text
PRIORITY CLAIM
The present non-provisional Application claims priority under 35
USC .sctn.119(e) from U.S. Provisional Patent Application having
Ser. No. 60/469,519, filed on May 9, 2003, by Dugas et al. and
titled SERVO FORMAT FOR AZIMUTH RECORDING; U.S. Provisional Patent
Application having Ser. No. 60/509,031, filed on Oct. 6, 2003, by
Dugas et al. and titled SERVO FORMAT FOR AZIMUTH RECORDING; and
U.S. Provisional Patent Application having Ser. No. 60/469,517,
filed on May 9, 2003, by Dugas et al. and titled SERVO BAND WITH
ZIGZAG TRANSITIONS FOR AZIMUTH RECORDING IN LINEAR TAPE; wherein
each of these provisional Applications is commonly owned by the
assignee of the present application and wherein the entire contents
of each is incorporated herein by reference.
Claims
What is claimed is:
1. A servo writing head that generates a magnetic flux for
producing one or more servo patterns in a data storage medium, the
head comprising a zigzag servo writing gap, wherein the zigzag
servo writing gap comprises at least three legs of a zigzag
pattern, wherein said head is writing azimuthal servo information
onto a data storage medium such that each leg of the zigzag pattern
is associated with a respective servo track of a common servo band;
and said head further comprising a second kind of servo writing
gap, wherein the zigzag servo writing gap and the second kind of
servo writing gap are capable of being independently subjected to
magnetic flux energy.
2. The servo writing head of claim 1, wherein the second kind of
servo writing gap comprises a chevron pattern.
3. The servo writing head of claim 1, wherein the second kind of
servo writing gap comprises first and second opposed chevron
patterns.
4. The servo writing head of claim 1, wherein the second kind of
servo writing gap comprises at least one leg parallel to at least
one leg of the zigzag servo writing gap, wherein each leg of the
zigzag servo writing gap has a cross-band length, and wherein the
parallel leg of the second servo writing gap has a cross-band
length that is at least as long as the total cross-band length of
at least two of the zigzag legs.
5. The servo writing head of claim 1, wherein the head further
comprises: (a) a magnetically permeable core having a nonmagnetic
sub-gap core in a manner such that the magnetically permeable core
comprises a first pole and a second pole; (b) a magnetically
permeable layer that spans from the first pole to the second pole
and has a region that overlies the sub-gap core; and (c) an
electrically conductive coil operationally engaging the
magnetically permeable core; and wherein the zigzag servo writing
gap is positioned within the region of the magnetically permeable
layer that overlies the sub-gap core.
6. The servo writing head of claim 5, wherein the electrically
conductive coil comprises a thin film coil.
7. The servo writing head of claim 1, wherein the zigzag servo
writing gap comprises first and second ends, wherein at least one
of said ends comprises a non-rectilinear gap termination
feature.
8. The servo writing head of claim 7, wherein the non-rectilinear
gap portion has a generally elliptical contour.
9. A method of writing servo features on a data storage medium,
comprising the steps of: (a) providing a servo writing head that
comprises at least one zigzag servo writing gap and a second kind
of servo writing gap, wherein the zigzag servo writing gap and the
second kind of servo writing gap are capable of being independently
subjected to magnetic flux energy, and wherein the zigzag servo
writing gap comprises at least three legs of a zigzag pattern; and
(b) using the zigzag servo writing gap and the second kind of servo
writing gap of the head to create servo tracks of a common servo
band on a data storage medium, each servo track comprising
azimuthal servo transitions associated with a respective leg of the
zigzag pattern and additional servo transitions associated with the
second kind of servo writing gap.
10. The method of claim 9, wherein said step (b) comprises
energizing the head in a manner effective to write a sequence of
zigzag magnetic flux patterns at a mono-frequency at least within a
track following sector of the servo band.
11. The method of claim 9, wherein the azimuthal servo transitions
are written in a manner effective to provide track following
information and wherein the additional servo transitions are
written in a manner effective to provide information indicative of
track identity.
12. The method of claim 9, wherein the azimuthal servo transitions
are written in a manner effective to provide track following
information and wherein the additional servo transitions are
written in a manner effective to provide information indicative of
data group identity.
13. The method of claim 9, wherein the azimuthal servo transitions
are written in a manner effective to provide track following
information and wherein the additional servo transitions are
written in a manner effective to provide information indicative of
track and data group identity.
14. The method of claim 9, wherein the head comprises a plurality
of the zigzag servo writing gaps and wherein step (b) comprises
using the head to write zigzag servo transitions in a plurality of
servo bands of the data storage medium.
15. The method of claim 9, wherein the data storage medium is a
magnetic recording tape.
16. The method of claim 9, wherein the head comprises a thin film,
electrically conductive coil incorporated in the head in a manner
effective to help generate a magnetic flux pattern used to write
the zigzag servo transitions.
17. A method of forming a servo band on a data storage medium,
comprising the steps of providing a servo writing head that
generates magnetic fluxes for producing a plurality of servo
patterns in a data storage medium, the head comprising a zigzag
servo writing gap and a second kind of servo writing gap, wherein
the zigzag servo writing gap and the second kind of servo writing
gap are capable of being independently subjected to magnetic flux
energy, and wherein the zigzag servo writing gap comprises at least
three legs of a zigzag pattern; and using the zigzag servo writing
gap to write an azimuthal style servo pattern into at least a
portion of a plurality of servo tracks of at least one common servo
band on the data storage medium and using the second kind of servo
writing gap to write additional servo features in the common servo
band.
18. A compound servo writer head, comprising: (a) a first servo
writing portion comprising: (i) a substrate, comprising: (1) first
and second sub-pole members; and (2) a sub-gap member interposed
between the first and second sub-pole members; (ii) a magnetically
permeable layer formed over the substrate such that said
magnetically permeable layer overlies the first and second sub-pole
members and the sub-gap member; (iii) at least a first servo
writing gap pattern formed in a portion of the magnetically
permeable layer overlying the sub-gap member; and (iv) an
electrically energized thin film coil to provide magnetic flux to
the sub-pole in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium. (b) a second servo writing portion comprising:
(i) a substrate, comprising: (1) first and second sub-pole members;
and (2) a sub-gap member interposed between the first and second
sub-pole members; (ii) a magnetically permeable layer formed over
the substrate such that said magnetically permeable layer overlies
the first and second sub-pole members and the sub-gap member; (iii)
at least a second servo writing gap pattern formed in a portion of
the magnetically permeable layer overlying the sub-gap member; and
(iv) an electrically energized thin film coil to provide magnetic
flux to the sub-pole in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium; and wherein each of the first and second servo
writing gap patterns is independently energizable.
19. The compound servo writer head of claim 18, wherein the coil of
the second servo writing portion comprises a thin film coil.
20. The compound servo writer head of claim 18, wherein the first
and second servo writing gap patterns are in the same channel.
21. The compound servo writer head of claim 18, wherein the head
comprises a plurality of channels.
22. The compound servo writer head of claim 18, wherein the first
servo pattern comprises a zigzag pattern having at least three
legs.
23. A method of recording servo information, comprising the steps
of providing a compound servo writer head, comprising: (a) a first
servo writing portion comprising: (i) a substrate, comprising: (1)
first and second sub-pole members; and (2) a sub-gap member
interposed between the first and second sub-pole members; (ii) a
magnetically permeable layer formed over the substrate such that
said magnetically permeable layer overlies the first and second
sub-pole members and the sub-gap member; (iii) at least a first
servo writing gap pattern formed in a portion of the magnetically
permeable layer overlying the sub-gap member; and (iv) an
electrically energized thin film coil to provide magnetic flux to
the sub-pole in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium. (b) a second servo writing portion comprising:
(i) a substrate, comprising: (1) first and second sub-pole members;
and (2) a sub-gap member interposed between the first and second
sub-pole members; (ii) a magnetically permeable layer formed over
the substrate such that said magnetically permeable layer overlies
the first and second sub-pole members and the sub-gap member; (iii)
at least a second servo writing gap pattern formed in a portion of
the magnetically permeable layer overlying the sub-gap member and
that is independently energizable with respect to the first servo
writing portion, said second servo writing portion; and (iv) an
electrically energized coil to provide magnetic flux to the
sub-pole in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium; and using the compound servo writer head to
write servo information in a data storage medium.
24. The method of claim 23, wherein said using step comprises
writing at least one servo band on a data storage medium, wherein
the servo band comprises a plurality of azimuth style servo
tracks.
25. The method of claim 24, wherein said azimuth style servo tracks
are written in at least one track following sector and wherein the
servo band further comprises a sector selected from the group
consisting of a track ID sector, a data group ID sector, and a
track and data group ID sector.
26. The method of claim 23, wherein said servo information
comprises amplitude based servo features and time based servo
features.
27. The method of claim 26 wherein said amplitude and time based
servo features are written into different sectors of a servo
band.
28. The method of claim 26, wherein said amplitude and time based
servo features are written into the same sector of a servo
band.
29. A compound servo writer head, comprising: (a) a first servo
writing portion comprising: (i) a substrate, comprising: (1) first
and second sub-pole members; and (2) a sub-gap member interposed
between the first and second sub-pole members; (ii) a magnetically
permeable layer formed over the substrate such that said
magnetically permeable layer overlies the first and second sub-pole
members and the sub-gap member; (iii) at least a first servo
writing gap pattern formed in a portion of the magnetically
permeable layer overlying the sub-gap member; and (iv) an
electrically energized coil to provide magnetic flux to the
sub-pole in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium; and (b) a second servo writing portion
comprising: (i) a substrate, comprising: (1) first and second
sub-pole members; and (2) a sub-gap member interposed between the
first and second sub-pole members; (ii) a magnetically permeable
layer formed over the substrate such that said magnetically
permeable layer overlies the first and second sub-pole members and
the sub-gap member; (iii) at least a second servo writing gap
pattern formed in a portion of the magnetically permeable layer
overlying the sub-gap member; and (iv) an electrically energized
coil to provide magnetic flux to the sub-pole in a manner such that
a magnetic flux pattern corresponding to the servo writing gap
pattern can be written in a data storage medium; and wherein each
of the first and second servo writing gap patterns is independently
energizable.
30. The compound servo writer head of claim 29, wherein the first
and second servo writing gap patterns are in the same channel.
31. The compound servo writer head of claim 29, wherein the head
comprises a plurality of channels.
32. The compound servo writer head of claim 29, wherein the first
servo pattern comprises a zigzag pattern having at least three
legs.
33. A method of recording servo information, comprising the steps
of providing a compound servo writer head, comprising: (a) a first
servo writing portion comprising: (i) a substrate, comprising: (1)
first and second sub-pole members; and (2) a sub-gap member
interposed between the first and second sub-pole members; (ii) a
magnetically permeable layer formed over the substrate such that
said magnetically permeable layer overlies the first and second
sub-pole members and the sub-gap member; (iii) at least a first
servo writing gap pattern formed in a portion of the magnetically
permeable layer overlying the sub-gap member; and (iv) an
electrically energized coil to provide magnetic flux to the
sub-pole in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium; and (b) a second servo writing portion
comprising: (i) a substrate, comprising: (1) first and second
sub-pole members; and (2) a sub-gap member interposed between the
first and second sub-pole members; (ii) a magnetically permeable
layer formed over the substrate such that said magnetically
permeable layer overlies the first and second sub-pole members and
the sub-gap member; (iii) at least a second servo writing gap
pattern formed in a portion of the magnetically permeable layer
overlying the sub-gap member and that is independently energizable
with respect to the first servo writing portion, said second servo
writing portion; and (iv) an electrically energized coil to provide
magnetic flux to the sub-pole in a manner such that a magnetic flux
pattern corresponding to the servo writing gap pattern can be
written in a data storage medium; and using the compound servo
writer head to write servo information in a data storage
medium.
34. The method of claim 33, wherein said using step comprises
writing at least one servo band on a data storage medium, wherein
the servo band comprises a plurality of azimuth style servo
tracks.
35. The method of claim 34, wherein said azimuth style servo tracks
are written in at least one track following sector and wherein the
servo band further comprises a sector selected from the group
consisting of a track ID sector, a data group ID sector, and a
track and data group ID sector.
36. The method of claim 32, wherein said servo information
comprises amplitude based servo features and time based servo
features.
37. The method of claim 36 wherein said amplitude and time based
servo features are written into different sectors of a servo
band.
38. The method of claim 36, wherein said amplitude and time based
servo features are written into the same sector of a servo band.
Description
FIELD OF THE INVENTION
The present invention relates generally to data storage reading,
writing, and erasing systems, techniques, and devices incorporating
servo capabilities and features. In particular, the present
invention relates to systems incorporating azimuthal servo features
and corresponding head configurations, especially for use in
reading, writing, and erasing operations for achieving high
recording densities.
BACKGROUND OF THE INVENTION
Various data recording, playback, and erasing techniques exist for
recording data to and from data storage media, such as magnetic
tape. Magnetic tapes are used for data storage in computer systems
requiring data removability, low-cost data storage, high data-rate
capability, and high volumetric efficiency and reusability. The
rapidly accelerating growth in stored digital data and images, the
Internet, and replacement of paper as long-term record retention,
and the need for massive dense storage for reconnaissance and
surveillance is creating a demand for corresponding increases in
the data storage capacities of magnetic tape recording and
reproducing systems, while maintaining the special requirements of
high speed digital tape systems.
Tape recording and reproducing systems for use as computer data
storage devices are often required to provide high data transfer
rates and to perform a read check on all written data. To satisfy
these requirements, conventional, orthogonal linear tape systems
(where recorded transition lines that are created between regions
of opposite magnetization are orthogonal to the head/tape motion
direction) typically employ methods wherein the tracks of data lie
parallel to each other and to the edge of the tape. Linear
recording techniques offer high data transfer rates by employing
reading and writing head configurations with multiple, parallel
channels, wherein each read and write head pair provides a channel,
typically with each writing or reading element in data transfer
contact with the recording media a substantial portion of the
time.
In orthogonal linear tape recording systems, data tracks generally
are followed in the direction of tape movement with the read and
write heads arranged in the same manner as the recorded transitions
that are perpendicular to the direction of tape motion. The writer
element to a significant degree defines the width of a data track
(and thus the number of data tracks that can be provided across a
tape of given width) by creating the regions or domains of
magnetization following one another in the tape direction at the
width of the write head.
The potential for misregistration of the read element to the
written track (from tape wander, data track alignment or the like)
requires in some systems that the read element be substantially
smaller than the written track width in order to ensure that the
read head is reading magnetization fields only within the desired
data track. Thus, the read head element also (as is also limited by
read head performance characteristics) limits how narrow the data
track can be, and hence the maximum track density.
Not only is the data track width limited by the minimum read
element size in order to meet the recording system's performance
criterion, it also is limited to accommodate expected
misregistration as may occur under the dynamic conditions of moving
media and as may be determined empirically or by modeling. If a
read head moves off the data track for whatever reason and begins
to read a signal from the adjacent track, the possibility of
erroneous data transfer increases. More specifically, the error
rate is known to increase exponentially as the read head moves
further off the data track. Typically, for an acceptable off-track
error rate, the adjacent track signal must be less than ten percent
of the data track signal being read.
The general premise is thus to write wide and read narrow. Writing
wide, however, decreases the data density (less data tracks across
a given tape width). Reading narrow is unfortunately limited by
making an acceptable read element that will still meet signal
amplitude, SNR (signal to noise ratio), and media defect
sensitivity requirements. As a result, minimum track width is
approximately the width of a read element that meets the above
performance requirements plus twice the misregistration (normally
the three sigma value since the misregistration is a statistical
distribution).
There are a number of potential sources of read element to written
track misregistration error, which error is systematic in that both
the media and the drive are involved as potential sources of error.
The principal sources of error include tape lateral motion,
vibration in the head/actuator assembly, dimensional instability of
the media substrate, and mechanical misalignments between read and
write elements in manufacturing and assembly. Probably the most
significant limitation on tape track densities is the tendency for
the tape to experience lateral tape motion, which is a tendency for
the tape to shift laterally relative to the linear direction of
tape motion. During a data track write, lateral tape motion can
cause one or more data tracks to deviate from a desired axis along
which tracks are expected to be written. During reading, lateral
tape motion can cause misregistration of the read head over the
track being read. This build-up of potential misregistration of
data tracks combined with other less significant potential sources
of misregistration can result in a portion of the read element to
be positioned over an adjacent data track, which, if significant
enough, can cause an unacceptable level of data transfer errors. As
noted above, the reading of an adjacent track is typically limited
to ten percent or less of the desired data track signal. The normal
method in linear tape recording to ameliorate the potential effects
of this misregistration is to make the read element much narrower
than, i.e., approximately half, the track width. However, as noted
above, limitations of minimum signal amplitude,
signal-to-noise-ratio, and sensitivity to media defects provides a
lower limit as to how narrow the read element can actually be.
Thus, from a practical design perspective, an effective read head
size as determined by such performance constraints would be doubled
to determine a desirable data track width. As such, the effective
read element size limits how narrow a data track can be made.
One developed method of increasing data track density involves
azimuth recording techniques. Azimuth recording for data tracks has
long been used in helical recording systems and has been more
recently introduced into linear tape systems. Generally, in azimuth
recording of either helical or linear tape systems, data
transitions on alternate adjacent tracks are recorded at a similar
but opposite azimuth angle (e.g., .theta. on one track and -.theta.
on an adjacent track, with this alternating azimuth pattern
repeating across the data band) and relative to an axis along which
the head travels relative to the media. In helical tape recording
systems, the head is moved relative to a linear tape movement at a
significantly greater speed and at an angle to the relative
direction of tape movement.
Azimuth recording itself is a well-understood technology that
provides a level of suppression of an adjacent track signal. The
suppression is based upon the well known relationship that the
suppression, S=20*log 10[sin x/x], where x=(.pi.W/.lamda.)*tan
2.theta.. In this relationship W is the data track width, .theta.
is the positive value of the+/-.theta. angles that the recorded
transitions make with the transverse axis to the head direction,
and ( is the wavelength associated with the minimum transition
density (.lamda.=two times the maximum transition spacing). Thus, a
determined azimuth angle, .theta., is dependent on factors such as
the degree of suppression to be attained, the data track width W,
and the minimum transition density or maximum .lamda. of the
readback signal spectra. In current systems the data track width W
is at least an order of magnitude larger than .lamda. and thus, a
suitable transition angle .theta. can be relatively small to
achieve sufficient suppression of an adjacent data track
signal.
Because of such angular azimuth recording, a signal from a track
adjacent to the data track being read can be sufficiently
suppressed to an acceptable level, such as to be less than ten
percent of the data track signal as noted above. Hence, a read
element can overextend an adjacent track and thus can be designed
to be wider than the data track, allowing the full data track
signal to be utilized. Azimuth style recording for data tracks is
further described in Assignee's co-pending U.S. patent application
having Ser. No. 10/793,502, filed Mar. 4, 2004, in the names of
Dugas et. al., and titled Large Angle Azimuth Recording and Head
Configurations, the entirety of which is incorporated herein by
reference; as well as in U.S. Pat. No. 4,539,615, "Azimuthal
Magnetic Recording and Reproducing Apparatus."
Some current linear serpentine tape drives for azimuth recording
typically utilize a single head structure that contains two pairs
of read and write elements. Like orthogonal head structures,
azimuthal head structures are typically designed with the read and
write elements parallel to each other and aligned in the direction
of tape movement when brought into the proper alignment with the
desired azimuth angle. Thus, by offsetting the read and write
elements as they are positioned along lines that are parallel to
one another as to the distance along the parallel lines, an
orthogonally constructed head can be positioned to record and read
azimuthal tracks when rotated at an appropriate angle. The read and
write elements can be aligned so that with the proper spatial
relationship between them, they are able to read and write adjacent
tracks and only require transversal repositioning once for every
track pair. Such transversal movement and positioning or tracking
can be conventionally controlled by known actuators. Tracking can
be achieved in a single head, but usually requires the additional
complexity and weight of a dual degree freedom actuator, such as
conventionally known and that permits both rotary movement of the
single head and movement of the head in the transverse direction to
the tape movement. A compound dual degree freedom of motion
actuator, i.e. a single unit to provide multiple types of motion,
adds additional mass and generally needs to carry twice as many
leads in order to accommodate forward and reverse read and write
capabilities. This provision of additional leads adds stiffness to
the system that can inhibit or interfere with its motion
capabilities.
Recent generations of multi-channel linear serpentine tape systems
have used servo tracking to decrease track misregistration. The use
of servo tracking has greatly reduced tracking errors due to
manufacturing alignment and offset tolerances between the read and
write element arrays, skew errors, some track shift due to tape
substrate dimensional instability, and the effect of lateral tape
motion. In such systems, position sensing read sensors (servo
elements) detect prewritten servo tracks on the tape that can be
laid down under tightly controlled conditions to reduce
misalignment of the servo tracks to the tape. The tape is typically
divided into alternating bands of data tracks and servo tracks
where the band of data tracks can be much wider than the servo
band; typically the data band is 8 to 16 times the width of the
servo band, depending on the number of data channels. From the
output signals of the servo data elements, a position error signal
can be determined that is used by the servo control loop to
dynamically and more accurately position the data elements over
their tracks. Typically, the servo elements are located in the same
array as the read elements and can be symmetrically placed outboard
of the read array on each side.
Notwithstanding the widespread use of servo systems and formats, in
helical recording the Position Error Signal (PES) generally has
been embedded in the data-recording band and uses the data read
head as the servo transducer. Also, when recording or writing, the
head moves in only one direction relative to the tape and the tape
is only moving in one direction. Quantum Corp., for example, has
used azimuthal recording in its DLT drives, but does not track
follow.
A number of different encoding schemes have been proposed for servo
formats. The four most prevalent forms of encoding are frequency
encoding, amplitude encoding, time-base encoding, and phase
encoding. All tend to share a common characteristic where the servo
transducer is a single element. Further, except for time-based
encoding, the primary characteristic of these approaches is that
the encoded servo features on alternate servo tracks are different.
In some cases this differentiation can be extended to more tracks
to provide either a larger capture range when accessing the track
or enhancing track identification.
Most current servo systems used commercially in linear serpentine
tape systems commonly employ either an amplitude modulated
mono-frequency signal (AM system) or a "Time Base" system. A
typical AM system might utilize a single servo read element to
detect the position error signal where the "on track" PES is half,
or less, than the data signal. The weaknesses of the AM approach
include the susceptibility of the PES to dropouts and noise, the
reduced sample rate, the wider band width to accommodate the
modulation, and without writing (erasing the holes) the tracks
individually, the inability to identify the selected track.
Time-based servo position error signals have been introduced by IBM
in some of its latest products and the philosophy has been extended
to the LTO family drives that are being produced by IBM, Seagate,
and HP. Time-based servos use slightly (typically 6 7 degrees) but,
oppositely angled transitions for the servo timing features, e.g.,
"diamond-shaped," "vee," "inverted vee" features, combinations of
these, or the like. The time difference among servo transitions as
a function of transverse position of the servo head on tape
provides the positioning information. The servo transducer
orientation is nominally perpendicular to the track direction so
that the transitions are encountered at a slight angle.
Hybrid thin film/ferrite servowriter heads with precision patterns
have been developed to record the time-based servo tracks for IBM
and LTO tape heads. See, e.g., U.S. Patent Publication
2003/0016446, incorporated herein by reference in its entirety.
See, also, U.S. Pat. Nos. 6,496,328 and 6,269,533, and U.S.
Published Applications 2001/0003862; 2001/0045005; 2002/0171974;
and 2003/0039063; all of which are incorporated by reference herein
in their entireties.
A typical Time Base system might use a servo read element much
narrower than the track width or data read elements, hence a much
lower signal level and signal-to-noise ratio (SNR), while trying to
achieve a high spatial resolution. Neither system typically
provides positive track identification, although the Time Based
system could allow servo group identification.
A significant advantage of the "Time Based" Servo approach is that
it is relatively insensitive to dropouts and Gaussian noise.
However, because of the narrowness of the servo transducer, the
signal to noise ratio (SNR) is quite low. Perturbation along the
axis of the tape in the transitions is magnified in the transverse
direction by 1/sin(, where ( is the azimuth angle of the
transitions. Thus, with an azimuth angle of about 6 degrees to 7
degrees, perturbation is magnified by a factor of about ten.
Further, although the measurement is insensitive to any static
variation in the tape speed, significant error may tend to be
introduced by any dynamic variation in the tape speed. Like the AM
system, this approach typically does not provide for unique
identification of the data track. Further, modeling and simulation
have shown that the current time-based approaches may be limited to
intrinsic (to the servo pattern and head only) misregistrations of
several tenths of micron, thus limiting maximum track density to
4,000 6,000 tracks per inch.
With the trend toward recording higher densities, the industry
strongly needs a servo format and system that allows increasingly
more accurate on track guidance. It would be further desirable to
have a servo format and system that allows positive track and group
identification at the beginning, end, and optionally periodically
along the length of a tape.
SUMMARY OF THE INVENTION
The present invention provides improved methods and systems for
data recording and reading for increasing overall tape data storage
density, especially for data written in azimuth style. The
principles of the invention provide servo formats and systems that
allow accurate on track guidance for higher density applications
and that are less sensitive to off track error. Preferred
embodiments of the invention offer servo formats and systems of the
invention that allows positive track and group identification at
the beginning, end, and optionally periodically along the length of
a tape.
The present invention offers one or more strategies that may be
used singly or in combination to achieve one or more of such goals.
Firstly, the present invention provides azimuthal servo formatting
in which one or more servo bands contain multiple servo tracks
where the transitions on adjacent servo tracks are written at
opposing, azimuthal angles (i.e., positive and negative azimuth
angles) relative to a perpendicular to the tape path. The
correspondingly active servo and data transducers preferably are
co-linear with each other when parallel to the azimuthal
transitions. The servo band is desirably positioned functionally
proximate to at least one corresponding data group to assist
tracking during data record, write, and/or erase operations. The
data group preferably includes data tracks grouped functionally
into one or more data bands, wherein the data tracks also are
preferably written in azimuth style.
Further, servo systems of the invention optionally use centertapped
servo read heads. In one representative embodiment a single
centertapped head with at least two servo sensors is used for on
track guidance in at least one associated data group. In another
representative embodiment, two non-centertapped or centertapped
heads may be utilized in a pair of servo bands sandwiching an
associated data group. The centertapped heads may be centered over
the servo track of interest. The centertapped heads may be offset
or large enough so as to straddle a servo track boundary inasmuch
as the signal on adjacent servo tracks is suppressed due to the
azimuth character of the servo tracks.
Third, and counter-intuitively, the servo track pitch, centertap
width, and/or centertap sensor widths may be increased relative to
conventional practice to improve data density. For instance, the
centertap width may be arbitrarily wide so as to allow the two
sensors of a centertapped servo head to detect signals from two
nonadjacent servo tracks. With this approach, the data tracks can
have a pitch that is a fraction of the servo track pitch, helping
to facilitate high density data recording, playback, and erasing.
Additionally, a higher quality servo signal is obtained by using
relatively large servo track pitches and servo sensors. This aspect
of the invention is particularly preferred in data storage systems
whose media incorporate servo tracks written at the same or
different azimuth angles.
The present invention further provides in some embodiments a servo
system incorporating two or more classes (e.g., amplitude,
frequency, time-base, phase, etc.) of servo encoding schemes
incorporated into a servo band of a data storage medium. In
preferred embodiments, azimuthal servo transitions provide an
amplitude based scheme for servo guidance, and time-based
transitions help to provide positive track and or group
identification. The combination of AM and time-based encoding
schemes not only offers known advantages of each while eliminating
many drawbacks, but also offers unique advantages not achieved by
either scheme alone.
Furthermore, servowriter heads are described that are capable of
recording such servo patterns on a data storage medium.
In one aspect, the present invention relates to a servo writing
head that generates a magnetic flux for producing one or more servo
patterns in a data storage medium. The head comprises a zigzag
servo writing gap, wherein the zigzag servo writing gap comprises
at least three legs of a zigzag pattern. The aspect further relates
to a method of using this servo head write an azimuthal style servo
pattern into at least a portion of at least one servo band on the
data storage medium.
In another aspect, the present invention relates to a method of
writing servo features on a data storage medium, comprising the
steps of: (a) providing a servo writing head that comprises at
least one zigzag servo writing gap, wherein the zigzag servo
writing gap comprises at least three legs of a zigzag pattern; and
(b) using the head to create corresponding zigzag servo transitions
constituting at least a portion of a servo band of the data storage
medium.
In another aspect, the present invention relates to a data storage
medium comprising at least one servo band and at least one data
band, wherein the servo band comprises a plurality of servo tracks,
each of said servo tracks comprising azimuthal servo transitions
having an azimuthal orientation that alternates from servo track to
adjacent servo track. In another aspect, the present invention
relates to a method of recording data on a data storage medium,
comprising the steps of: (a) providing a data storage medium
comprising at least one servo band having a plurality of servo
tracks, each of said servo tracks comprising azimuthal servo
transitions having an azimuthal orientation that alternates from
servo track to adjacent servo track; and (b) recording data onto
one or more data tracks of the data storage medium in a manner such
that the data tracks comprise azimuthal data transitions having an
azimuthal orientation that alternates from servo track to adjacent
servo track.
In another aspect, the invention relates to a method of reading
data on a data storage medium, comprising the steps of: (a)
providing a data storage medium comprising (i) at least one servo
band and at least one data band, wherein the servo band comprises a
plurality of servo tracks, each of said servo tracks comprising
azimuthal servo transitions having an azimuthal orientation that
alternates from servo track to adjacent servo track, and (ii) at
least one data band comprising a plurality of data tracks; (b)
deriving a servo signal from the servo band; and (c) using
information comprising the servo signal to assist in reading data
from at least one of the data tracks.
In another aspect, the present invention relates to a tape
cartridge that includes a cartridge housing; and a data storage
medium contained in the cartridge housing, wherein the data storage
medium comprises at least one servo band and at least one data
band, wherein the servo band comprises a plurality of servo tracks,
each of said servo tracks comprising azimuthal servo transitions
having an azimuthal orientation that alternates from servo track to
adjacent servo track.
In another aspect, the present invention relates to a servo pattern
writing apparatus, comprising a servo writing head that generates a
magnetic flux for producing one or more servo patterns in a data
storage medium, the head comprising a zigzag servo writing gap,
wherein the zigzag servo writing gap comprises at least three legs
of a zigzag pattern.
In another aspect, the present invention relates to a servo writer
head, comprising: (a) a substrate, comprising: (i) first and second
sub-pole members; and (ii) a sub-gap member interposed between the
first and second sub-pole members; (b) a magnetically permeable
layer formed over the substrate such that said magnetically
permeable layer overlies the first and second sub-pole members and
the sub-gap member; (c) at least a first servo writing gap pattern
formed in a portion of the magnetically permeable layer overlying
the sub-gap member; and (d) a thin film coil energizingly coupled
to the substrate in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium. This aspect of the present invention also
relates to a method of using this head to write servo information
in a data storage medium.
In another aspect, the present invention relates to a compound
servo writer head, comprising: (a) a first servo writing portion
comprising: (i) a substrate, comprising: (1) first and second
sub-pole members; and (2) a sub-gap member interposed between the
first and second sub-pole members; (ii) a magnetically permeable
layer formed over the substrate such that said magnetically
permeable layer overlies the first and second sub-pole members and
the sub-gap member; (iii) at least a first servo writing gap
pattern formed in a portion of the magnetically permeable layer
overlying the sub-gap member; and (iv) a thin film coil
energizingly coupled to the substrate in a manner such that a
magnetic flux pattern corresponding to the servo writing gap
pattern can be written in a data storage medium. (b) a second servo
writing portion comprising: (i) a substrate, comprising: (1) first
and second sub-pole members; and (2) a sub-gap member interposed
between the first and second sub-pole members; (ii) a magnetically
permeable layer formed over the substrate such that said
magnetically permeable layer overlies the first and second sub-pole
members and the sub-gap member; (iii) at least a second servo
writing gap pattern formed in a portion of the magnetically
permeable layer overlying the sub-gap member; and (iv) a coil
energizingly coupled to the substrate in a manner such that a
magnetic flux pattern corresponding to the servo writing gap
pattern can be written in a data storage medium. This aspect of the
invention also relates to a method of recording servo information,
comprising the step of using the servo writer head of claim 18 to
write servo information in a data storage medium.
In another aspect, the present invention relates to a compound
servo writer head, comprising: (a) a first servo writing portion
comprising: (i) a substrate, comprising: (1) first and second
sub-pole members; and (2) a sub-gap member interposed between the
first and second sub-pole members; (ii) a magnetically permeable
layer formed over the substrate such that said magnetically
permeable layer overlies the first and second sub-pole members and
the sub-gap member; (iii) at least a first servo writing gap
pattern formed in a portion of the magnetically permeable layer
overlying the sub-gap member; and (iv) a coil energizingly coupled
to the substrate in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium; and (b) a second servo writing portion
comprising: (i) a substrate, comprising: (1) first and second
sub-pole members; and (2) a sub-gap member interposed between the
first and second sub-pole members; (ii) a magnetically permeable
layer formed over the substrate such that said magnetically
permeable layer overlies the first and second sub-pole members and
the sub-gap member; (iii) at least a second servo writing gap
pattern formed in a portion of the magnetically permeable layer
overlying the sub-gap member; and (iv) a coil energizingly coupled
to the substrate in a manner such that a magnetic flux pattern
corresponding to the servo writing gap pattern can be written in a
data storage medium. This aspect of the invention also relates to a
method of recording servo information, comprising the step of using
the servo writer head of claim 32 to write servo information in a
data storage medium.
In another aspect, the present invention relates to a method of
making a compound servo writing head, comprising the steps of: (a)
providing a substrate comprising first and second magnetically
permeable substrate portions; (b) forming a magnetically permeable
layer over the first and second magnetically permeable substrate
portions of the substrate, wherein the magnetically permeable layer
comprises first and second writing gap features associated with the
first and second substrate portions, respectively.
In another aspect, the present invention relates to a data storage
medium, comprising servo information, said servo information
including first and second kinds of encoded servo features.
In another aspect, the present invention relates to a data storage
cartridge, comprising: (a) a housing; and (b) a data storage medium
contained in the housing, said medium comprising servo information
that includes first and second kinds of encoded servo features.
In another aspect, the present invention relates to a data storage
system comprising: (a) a data storage medium comprising servo
information that includes first and second kinds of encoded servo
features and data information; (b) at least one servo sensor
operationally that engages the data storage medium in a manner
effective to read the servo information; and (c) at least one data
sensor operationally that engages the data storage medium in a
manner effective to read the data information.
Another aspect of the present invention relates to a method of
writing servo information onto a data storage medium, comprising
the steps of writing a first kind of servo information onto the
data storage medium that provides track following information and
writing a second kind of servo information onto the data storage
medium that provides identification information.
Another aspect of the present invention relates to a data storage
medium, comprising (a) a plurality of servo tracks; and (b) a
plurality of data tracks; and (c) wherein the data tracks have a
track pitch T.sub.d and the servo tracks have a track pitch
T.sub.s, wherein T.sub.s=mT.sub.d, wherein m is greater than 1. In
another aspect, the present invention relates to a data storage
system, comprising: (a) a data storage medium, comprising (i) a
plurality of azimuth style servo tracks having a track pitch
T.sub.s; and (ii) a plurality of azimuth style data tracks having a
track pitch T.sub.d wherein T.sub.s=mT.sub.d, wherein m is greater
than 1; (c) a first servo sensor that readingly engages the
plurality of servo tracks; and (d) a first data sensor that
readingly engages the plurality of data tracks.
Another aspect of the present invention relates to a method of
making a compound servo writer head, comprising the steps of: (a)
providing a first servo writer head portion, comprising: (i) first
and second sub-pole members; and (ii) a first sub-gap member
interposed between the first and second sub-pole members; (iii) a
first magnetically permeable layer formed over the first and second
sub-pole members and the first sub-gap member; (iv) at least a
first servo writing gap pattern formed in a portion of the
magnetically permeable layer overlying the first sub-gap member;
and (v) a first coil energizingly coupled to the substrate in a
manner such that a magnetic flux pattern corresponding to the first
servo writing gap pattern can be written in a data storage medium;
(b) providing a second servo writer head portion, comprising: (i)
third and fourth sub-pole members; and (ii) a second sub-gap member
interposed between the third and fourth sub-pole members; (iii) a
second magnetically permeable layer formed over the third and
fourth sub-pole members and the second sub-gap member; (iv) at
least a second servo writing gap pattern formed in a portion of the
magnetically permeable layer overlying the second sub-gap member;
and (v) a second coil energizingly coupled to the substrate in a
manner such that a magnetic flux pattern corresponding to the
second servo writing gap pattern can be written in a data storage
medium; and (c) mechanically assembling the first and second servo
writer head portions to form the compound head in a manner such
that the first and second servo writing gap patterns are in a
predetermined spatial relationship with respect to each other on a
data storage media engaging surface of the compound servo writer
head. This aspect of the invention also relates to a method of
recording servo information, comprising the step of using the servo
writer head to write servo information in a data storage
medium.
BRIEF DESCRIPTION OF THE DRAWINGS
The understanding of the above mentioned and other advantages of
the present invention, and the manner of attaining them, and the
invention itself can be facilitated by reference to the following
description of the exemplary embodiments of the invention taken in
conjunction with the accompanying drawings, wherein:
FIG. 1 is a schematic plan view of a portion of a data storage
system showing a thin film head engaging a magnetic recording tape
of the present invention, wherein the tape comprises a plurality of
servo and data features written in azimuth style.
FIG. 2 is a more detailed, schematic plan view of a portion of the
magnetic recording tape of FIG. 1, wherein the head is shown
engaging the tape in two alternate positions.
FIG. 3 schematically shows how the signal for adjacent, negative
(or positive) azimuth style servo and data transitions of the
magnetic recording tape shown in FIGS. 1 and 2 is suppressed when
the head sensors are oriented at an opposite, positive (or
negative) azimuth angle.
FIG. 4a schematically shows how a centertapped servo read head
detects a servo signal when centered over an underlying servo track
when the head and track are oriented at generally the same azimuth
angle.
FIG. 4b schematically shows how a centertapped servo read head
detects a servo signal when to the left of a centered position over
an underlying servo track when the head and track are oriented at
generally the same azimuth angle.
FIG. 4c schematically shows how a centertapped servo read head
detects a servo signal when to the right of a centered position
over an underlying servo track when the head and track are oriented
at generally the same azimuth angle.
FIG. 5 schematically shows an alternative embodiment of a data
storage system of the present invention in which a thin film
magnetic head is engaging a magnetic recording tape, wherein the
head is shown as engaging the tape in two alternate positions.
FIG. 6 schematically shows a perspective view of a portion of a
servo writer head containing a zigzag writing gap with, for
purposes of illustration, six legs for forming azimuth transitions
in a servo band containing six servo tracks.
FIG. 7a schematically shows a side view shown in cross section of a
data storage system of the present invention in which a
centertapped servo head and an associated data head engage a
magnetic recording tape, wherein the centertap is sufficiently wide
such that the servo sensors engage nonadjacent servo tracks.
FIG. 7b schematically shows a side view shown in cross section of a
data storage system of the present invention in which a
centertapped servo head and an associated data head engage a
magnetic recording tape, wherein the centertap is sufficiently wide
such that the servo sensors engage nonadjacent servo tracks,
wherein the servo track pitch is enlarged relative to the data
track pitch, and wherein the servo sensor widths are further
enlarged to generally correspond to the enlarged servo track
pitch.
FIG. 8 schematically shows a plan view of a data storage system of
the invention in which a thin film head is engaging a magnetic
recording tape, wherein the centertap is sufficiently wide such
that the servo sensors engage nonadjacent servo tracks, wherein the
servo track pitch is enlarged relative to the data track pitch, and
wherein the servo sensor widths are further enlarged to generally
correspond to the enlarged servo track pitch.
FIG. 9 schematically shows a plan view of a data storage system of
the present invention in which a thin film head with a wide
centertapped servo structure is shown engaging a magnetic tape in
five alternate positions.
FIG. 10 schematically shows a servo band of the present invention
having track guiding and track ID capabilities and incorporating a
hybrid encoding scheme including time based servo transitions and
amplitude based servo transitions.
FIG. 11 schematically shows a data storage medium of the present
invention comprising servo bands incorporating a hybrid encoding
scheme including time based servo transitions and amplitude based
servo transitions such that the servo band has track guiding and
track/group ID capabilities.
FIG. 12 schematically shows another embodiment of a data storage
medium of the present invention comprising servo bands
incorporating a hybrid encoding scheme including time based servo
transitions and amplitude based servo transitions such that the
servo band has track guiding and track/group ID capabilities.
FIG. 13 schematically shows a data storage medium of the present
invention comprising servo bands incorporating a hybrid encoding
scheme including time based servo transitions and amplitude based
servo transitions such that the servo band has track guiding and
track/group ID capabilities.
FIG. 14 schematically shows a servo band of the present invention
having track guiding and track ID capabilities and incorporating a
hybrid encoding scheme including time based servo transitions and
amplitude based servo transitions.
FIG. 15 schematically shows a perspective view of a portion of a
servo writer head containing an array of zigzag writing gaps and
opposed chevron writing gaps, wherein the head can be used to
create the servo band shown in FIG. 10.
FIG. 16 schematically shows a perspective view of a portion of an
alternative embodiment of a servo writer head having writing gaps
that provide servo bands with amplitude and time based features,
wherein portions of the head in between the servo bands are removed
for purposes of clarity.
FIG. 17 schematically shows a perspective view of a portion of an
alternative embodiment of a servo writer head having writing gaps
that provide servo bands with amplitude and time based features,
wherein portions of the head in between the servo bands are removed
for purposes of clarity.
FIG. 18 schematically shows a perspective view of a portion of an
alternative embodiment of a servo writer head having writing gaps
that provide servo bands with amplitude and time based features,
wherein portions of the head in between the servo bands are removed
for purposes of clarity.
FIG. 19 shows a portion of an alternative embodiment of a servo
writer head having relatively widely spaced writing gaps that
provide servo bands with amplitude and time based features.
FIG. 20 shows a portion of a servo band comprising transition
features formed by repeated pulsing of the servo writer head
according to FIG. 19.
DETAILED DESCRIPTION
The embodiments of the present invention described below are not
intended to be exhaustive or to limit the invention to the precise
forms disclosed in the following detailed description. Rather a
purpose of the embodiments chosen and described is so that the
appreciation and understanding by others skilled in the art of the
principles and practices of the present invention can be
facilitated.
FIGS. 1, 2, and 3 schematically show one embodiment of a data
storage system 10 of the present invention that combines azimuth
servo features, azimuth data features, and servo and data
transducers that are generally co-linear and/or are parallel to the
corresponding azimuthal transitions of the servo and data bands
during reading, writing, and erasing operations. System 10 is in
the exemplary form including a magnetic recording tape 12 (a
portion of the length being shown) that is readingly, writingly,
and erasingly coupled to read/write head 14.
Tape 12 includes one or more servo bands 16 and one or more data
groups 20 as components in a multi-channel, linear, serpentine tape
system. The number of servo bands 16 and data groups 20 may vary
depending upon factors such as the desired recording density, the
tape width, the servo scheme being used, separation of data
channels, and the like in accordance with conventional practices.
The number of servo bands 16 may be less than, the same as, or
greater than the number of data groups 20. Typical magnetic
recording tapes may include 4 to 50 data groups 20 and a
corresponding number of associated servo bands arranged in
data/servo groups across the full width of the tape 12. For
purposes of illustration, tape 12 as shown happens to include five
servo bands 16 and four data groups 20 arranged in four data/servo
groups 24a, 24b, 24c, and 24d.
In the particular preferred embodiment shown in FIGS. 1 though 3,
each data/servo group 24a, 24b, 24c, and 24d generally refers to a
data group 20 and the one or more associated servo bands 16 used to
assist track guidance in the data group 20 during data record,
write, and/or erase operations. The same servo band 16 may be
associated with more than one data group 20, and hence such servo
band 16 may be a member of more than one data/servo group. In
preferred embodiments as shown, a data group 20 shares a common
servo band 16 with one or more adjacent neighbor data group(s) 20
to form data groups 24a, 24b, 24c, and 24d. An alternative servo
scheme will be described below in which each data/servo group on a
tape includes a single servo band and a single, adjacent data band,
wherein a center-tapped servo head that engages the servo band is
used to assist tracking in the adjacent data group.
Still referring to FIGS. 1 through 3, but as best shown in FIG. 2,
each servo band 16 comprises a plurality of servo tracks 18. The
number of servo tracks 18 included in each servo band 16 need not
be the same as is used in the other servo tracks 18, but often each
servo band 16 incorporates the same number of servo tracks 18 to
ease the implementation of servo operations. The number of servo
tracks 18 to be used can vary over a wide range depending upon
factors noted above as well as the number of data channels, the
desired width of each servo band, the number of data transducers to
be simultaneously guided, and the like. Typical servo bands 16
might include 15 to 50 servo tracks 18. For purposes of
illustration, six are shown.
The servo tracks 18 include azimuthal servo transitions 26 and 28,
wherein transitions on adjacent servo tracks are written at
alternating azimuthal angles .theta. and .phi., respectively,
relative to a perpendicular to the length dimension of tape 12.
Generally, the angle .theta. of servo transitions 26 along a
particular servo track 18 is positive (or negative) while the angle
.phi. of servo transitions 28 on adjacent servo track(s) 18 is
negative (or positive). Most typically, .theta.=.phi. for practical
reasons, and the azimuth angle of the transitions in such instances
may simply be given by .theta., with the understanding that the
azimuth angle .theta. alternates from positive to negative from
track to track. The transitions 26 and 28 thus form zigzags, or
herringbone patterns, across the width dimensions of servo bands
16.
The magnitudes of the azimuth angles .theta. and .phi. may
independently vary over a wide range. Generally, if either of
.theta. and .phi. is too small, the desired degree of suppression
of servo signal from an adjacent track may be less than desired. If
the angle is too large, e.g., above about 45.degree. C., the angle
shifts practically from being positive to negative (or negative to
positive) such that the desired degree of suppression of the servo
signal from an adjacent track may be less than desired. As general
guidelines, the absolute magnitudes of .theta. and .phi.
independently may be in the range of from about 5 degrees to 45
degrees for one and from about -5 degrees to -45 degrees for the
other.
The present invention may be practiced in combination with large
angle azimuth recording (LAAZR) of servo and data transitions,
which is described in co-pending U.S. provisional application
titled Large Angle Azimuth Recording, filed Mar. 5, 2003, in the
names of Matthew P. Dugas and Theodore A. Schwarz and bearing
assigned Ser. No. 60/452,206, the entirety of which is incorporated
herein by reference. This practice is also described in assignee's
co-pending U.S. patent application Ser. No. 10/793,502, filed Mar.
4, 2004, titled LARGE ANGLE AZIMUTH RECORDING AND HEAD
CONFIGURATIONS, which is incorporated herein by reference in its
entirety.
The servo transitions 26 and 28 preferably can be recorded up to a
density comparable to the maximum data density. In this manner the
suppression of the servo signal from the adjacent servo tracks is
maximized. Preferably and as illustrated, the pattern of servo
transitions 26 and 28 is mono-frequency (density) among all servo
bands 16. This provides a very high sample rate, very narrow band
width, servo signal; a great amount of noise rejection capability
through oppositely biasing the servo elements creating a
differential position error signal, PES; very narrow bandpass
filtering; a high signal-to-noise-ratio, SNR; and good common-mode
noise and signal modulation rejection.
Although the azimuthal servo pattern preferably is a single
mono-frequency signal, it is possible to vary the density or
phasing of the transitions 26 and/or 28, e.g., to provide
manufacturing or tape location (along the track) information as is
done in the commercially well known LTO tape cartridge. Alternative
embodiments of the invention incorporating tape and track locating
features are described below.
Each data group 20 is further divided into a plurality of data
bands 21. Each data band 21 is further subdivided into a plurality
of data tracks 22. A data band 21 generally refers to a group of
data tracks 22 serviced by the same data sensor 42. For purposes of
illustration, each data group 20 includes four data bands 21. It is
recognized that there could more or less than four data bands 21 in
a data group 20. Typically, a data group 20 might include 8 to 16
track groups to achieve a high data/servo ratio for efficiency.
Similarly, the number of data tracks 22 included in each data band
21 can vary over a wide range, but typically is in the range of 50
to 500. For purposes of illustration, each data band 21 includes
six data tracks 22, which matches the number of servo tracks 18 in
an associated servo band 16. The ratio of servo tracks 18 to the
number of data tracks 22 in each data band 21 need not be 1:1 in
all cases. The ratio can be less than 1:1, for instance, as might
be the case when using a multi-channel servo head. Alternatively,
this ratio might be greater than 1:1 when using a centertapped
servo head.
Preferably, in a manner similar to servo tracks 18, it is preferred
that data tracks 22 also include azimuth style data transitions 36
and 38. The azimuth angles of transitions 36 and 38 preferably
match the azimuth angles of associated servo transitions 26 and 28,
respectively. Consequently, as a servo signal is being derived from
servo track(s) 18 having servo transitions recorded at a particular
azimuth angle, and as a consequence of the manner in which data
transducers are correspondingly angled in azimuth fashion during
tape operations, corresponding data signals may be obtained from a
plurality of data tracks 22 whose transitions are characterized by
generally the same azimuth angle as such servo track(s). Signals
from adjacent servo and data tracks 18 and 22 will tend to be
suppressed. See also the discussion of FIG. 3, below, where this
desirable suppression effect is discussed further.
Still referring collectively to FIGS. 1 through 3, but primarily to
FIG. 2, head 14 generally includes one or more servo transducers 40
and one or more data transducers 42. The servo and data transducers
40 and 42 preferably are co-linear and/or are parallel to the
azimuthal servo and data transitions being read, written, or
erased. Thus, the transducers 40 and 42 also preferably are
disposed at azimuthal angles relative to the tape 12. FIG. 2 shows
head 14 oriented in two azimuthal positions. In one position, the
sensors 40 and 42 in head 14 are aligned in azimuth fashion with
transitions 26 and 36. In the other position, the sensors 40 and 42
in head 14 are aligned in azimuth fashion with transitions 28 and
38. During reading, writing, and erasing operations, the servo
transducers 40 detect a servo signal with high signal to noise
characteristics from particular servo track(s) 18, with desirable
signal suppression from adjacent tracks having transitions at a
generally opposite azimuthal angle. Characteristics of the servo
signal are used with a suitable control algorithm to keep the servo
transducer heads 42 in proper registration with the servo track(s)
18 so that corresponding data transducer head(s) 42 remain properly
registered with corresponding data track(s) 22.
The tape 12 is bi-directional relative to head 14 along the length
dimension of tape 12 (as indicated by bi-directional arrow 15) so
that tape 12 can move past head 14 in either a first direction 17
or second direction 19. Head 14 also may be capable of relative
movement across width dimension of tape 12 so that the servo
transducer(s) 40 can engage additional servo track(s) 18 (and servo
bands 16) for corresponding registration of data transducers 42
with additional data tracks 22 (and data bands 18). Head 14 is
further capable of relative rotational movement in a range that
includes at least the two orientations of head 14 shown in FIG. 2.
This allows servo and data transducers 40 and 42 to be aligned with
positive (negative) transitions in one orientation and negative (or
positive) transitions in the other orientation. Alternately, two
separate, but identical heads oriented at alternate azimuth angles
may be employed.
FIG. 3 schematically illustrates the suppression of signals from
adjacent servo and data tracks when using the data recording system
10 of FIGS. 1, 2. FIG. 3 shows head 14 in an orientation such that
servo and data transducers 40 and 42 are generally aligned with
servo and data transitions 26 and 36 oriented at a positive (or
negative) azimuth angle. Because the servo and data transitions 28
and 38 on adjacent tracks are oriented at an opposite azimuth
angle, signals from those adjacent tracks are greatly suppressed.
This is shown schematically in FIG. 3 by the omission of the
transition features of those adjacent tracks.
FIGS. 1, 2, and 3 show an illustrative system 10 in which the servo
and data transducers 40 and 42 generally are centered over the
corresponding servo and data tracks 18 and 22 during reading,
writing, and erasing operations. A position error signal (PES) is
generated whose character generally depends upon the degree to
which the servo transducer(s) 40 drifts away from a centered
position over the servo track being engaged.
The particular embodiment shown in FIGS. 1, 2, and 3 illustrates a
servo scheme in which two servo transducers 40 in two, separate,
spaced apart servo bands 16 are used for track guidance in a data
band 24 positioned between the two servo bands 16. Either
centertapped and/or non-centertapped heads may be used for such
servo operations. "On-track" positioning is determined by balancing
or otherwise comparing the output of the two servo transducers 40.
Because of the spatial separation of the two servo transducers 40,
potential servo signal error can occur from at least two sources.
First, the individual transducers 40 can be dissimilar. Hence,
their amplitude characteristics and cross-track profiles might also
differ. Second, defects affecting one transducer 40 and not the
other could introduce an additional error factor. This can be
partially ameliorated by using the outputs of tranducers 40 as
sliding references so that if one is not changing, the position is
held. For instance, a position error signal might only be generated
if the outputs of both transducers 40 are changing in opposite
directions.
Consequently, a more preferred servo scheme involves using a
single, center-tapped, servo transducer preferably in a single
servo band 16 for track guidance in an adjacent data band 24. A
single servo transducer that is "split" or centertapped is able to
provide information of whether the transducer is off-track to the
right or to the left without requiring a separate servo transducer
in the same or different servo band. The amplitude of the signals
from the right and left halves are compared to produce the position
error signal. Centertapped magnetoresistive heads are well known,
such as the read transducers on the IBM Corporation 3480 head, to
the tape industry and have been described, for example, in U.S.
Pat. No. 5,079,663.
The approach of using a single, centertapped servo transducer to
generate a suitable servo signal without requiring the use of
additional servo heads on nonadjacent servo bands is shown
schematically in FIGS. 4a, 4b, and 4c. The suppression of servo
signals from adjacent servo tracks makes this approach very
accurate. FIGS. 4a, 4b, and 4c show data recording system 50 that
includes center-tapped servo read head 52 readingly engaging a
particular servo track 54 in a servo band 56 of magnetic recording
tape 58. Servo band 56 further includes at least other servo tracks
60, 62, 64, and 66.
Center-tapped servo read head 52 includes left lead 68, right lead
70, centertap 72, and sensors 73. Conductors 74 and 75 respectively
couple leads 68 and 70 to servo amplifiers/filters 78 and 80.
Centertap 72, conductor 76, and servo amplifiers/filters 78 and 80
are coupled to common ground 82. The amplitude of the signals from
the right and left halves are compared to produce the position
error signal. For example, in FIG. 4a, head 52 is centered over
servo track 54. The amplitudes of output signals 84a and 84b are
generally the same, indicative of the desired "on track" centered
position. In FIG. 4b, head 52 is left of center of servo track 54.
The amplitude of output signal 85a is greater than that of output
signal 85b, indicative of head 52 being left of center. In FIG. 4c,
head 52 is right of center of servo track 54. The amplitude of
output signal 86a is greater than that of output signal 86b,
indicative of head 52 being right of center.
FIGS. 1, 2, and 3 show a servo approach in which centertapped servo
transducer(s) are centered over a particular servo track when "on
track". FIG. 5 shows an alternative approach in which the servo
elements are not centertapped. System 150 includes head 152
engaging a data/servo group 163 constituting a portion of a
magnetic recording tape 154. Head 152 includes servo sensors 155
and 156. Head 152 also includes data sensors 157 and 158. Sensors
155, 156, 157, and 158 are co-linear. FIG. 5 shows head 152 in two,
alternate azimuthal positions.
Data/servo group 163 includes servo bands 159 and 160 and data
group 161. Each of servo bands 159 and 160 includes six azimuth
style servo tracks 162. Data group 161 includes two data bands 163,
each containing six azimuth style data tracks 164. Each of data
sensors 157 and 158 engage data tracks 164 in a corresponding data
band 163. Each of the servo sensors 155 and 156 is oppositely
offset by a half of a servo track width such that it is centered on
the junction of two opposite azimuth tracks. A servo signal is
readily detected from the underlying portion of the particular
servo tracks whose azimuthal transitions generally are aligned with
the servo transducers, while the signals from the adjacent,
underlying tracks (whose transitions are angled oppositely) are
suppressed.
FIG. 6 schematically illustrates one embodiment of a servowriter
head 100 that may be used to produce the azimuth style, or zigzag,
servo transitions of the present invention. Head 100 generally
comprises a layered structure including a suitable subgap layer 102
that is positioned between two poles 104 and 106. The subgap layer
102 may be made from a ceramic or other suitable nonmagnetic
material that may be thin film deposited. Poles 104 and 106 may be
made from a ferrite or other suitable magnetic material and may be
in the form of a thin film if desired. A magnetic thin film layer
108 overlies layers 102, 104, and 106. Servowriter pattern 110 is
formed in magnetic thin film layer 108 and has an azimuthal pattern
for forming corresponding, azimuthal, zigzag transitions across the
width of a servo band on a data recording medium. In this
embodiment, the pattern 108 contains six alternating azimuths for
forming six corresponding servo tracks. Head 100 is shown with only
one azimuthal pattern 108. In some applications, e.g., for high
track densities, wide tape, or few data channels, head 100 may
include a plurality of such patterns spaced apart across head 100
corresponding to the desired spacing and number of servo bands that
are desired.
Head 100, including any desired servo pattern(s), may be fabricated
in accordance with procedures described in U.S. Pat. Nos.
6,496,328; 6,269,533; as well as U.S. Published applications
2001/0003862; 2001/0045005; 2002/0171974; and 2003/0039063, each of
which is incorporated herein by reference in its entirety.
Additional kinds of servo heads that may be used in practicing some
embodiments of the present invention have been described in U.S.
Pat. Nos. 5,572,392 and 5,652,015, both of which are incorporated
herein by reference in their entireties. A particularly preferred
style of servo write head that may be used in the practice of the
present invention includes thin film sub-poles and thin film coils
and is described in Assignee's co-pending U.S. provisional patent
application titled Arbitrary Pattern Thin Film Surface Film Head in
the names of Dugas et. al., filed May 4, 2004, and having Ser. No.
60/568,139, the entirety of which is incorporated herein by
reference. Preferred structures used at the ends of writing gaps to
help write transitions more accurately with lesser stray writing
are described in U.S. Patent Application titled Patterned Magnetic
Recording Head with Termination Pattern Having Curved Portion,
naming as an inventor Matthew P. Dugas, filed Oct. 10, 2003, and
having Ser. No. 10/683,809, the entirety of which is incorporated
herein by reference.
As noted above, there are advantages to using a centertapped servo
read head to detect servo information from a single servo band.
However, previously, only non-centertapped heads have been used on
a widespread commercial basis in narrow data track situations
because of the required centertap width for effective current
carrying capability, resistance to signal loss, high signal to
noise ratio, manufacturability, and reliability. Centertapped servo
heads have tended to be too wide to pick up clean servo signals of
interest without also spanning, and thereby picking up undesired
signal information from, one or more adjacent servo tracks.
For example, a conventional servo head might be on the order of 2.8
micrometers wide to read conventional high density, servo tracks.
If such a servo head were centertapped, the centertap would need to
be around 0.7 micrometers wide to fit in a head of such dimensions.
This is too narrow to work effectively. For narrow tracks (<5
.mu.m) this results in reliability and current density problems in
the centertap. To achieve effective current carrying capability,
resistance to signal loss, high signal to noise ratio,
manufacturability, and reliability, a centertap typically is at
least 4 micrometers in width.
Consequently, there is some bias in the industry against using a
centertapped servo read head for servo operations in high density
data track situations. The present invention, however,
advantageously includes a number of features that singly or in
combination allow center-tapped servo read heads to be used
effectively to guide reading, writing, and erasing operations over
a wide range of low and high density data applications, but is
especially useful for high density data applications in which the
data track pitch, T.sub.d, is about five micrometers or less,
preferably about 0.5 to about 2 micrometers. Singly or in
combination, these features offer increased (e.g., doubled) signal
amplitude, increased capture range, and a higher signal to noise
ratio.
As one such feature, the azimuth (zigzag) character of the servo
transitions, especially when used in combination with a
centertapped servo read head canted at either the positive or
negative azimuth angle, as the case may be, is very useful in
facilitating the use of a centertapped servo head. Recall from the
discussion above that a read head oriented at a particular azimuth
will pick up a strong servo signal from an underlying servo track
having servo transitions recorded at a similar azimuth angle, but
will pick up very little signal from adjacent tracks written at the
opposite (positive v. negative) azimuth angle. Thus, a
center-tapped servo head can be wider than a particular azimuth
style servo track of interest.
The present invention also appreciates that a center-tapped servo
read head can span several servo tracks such that the servo sensors
pick up servo signals for comparison from two, nonadjacent servo
tracks. Preferably, the servo tracks of interest have servo
transitions with similar azimuth angles to each other, and the
servo sensors are generally canted at a similar azimuth angle so as
to minimize any signal detectable from intervening and/or adjacent
servo tracks. In short, the present invention appreciates that the
centertap of a center-tapped servo need not be narrow to guide data
reading, writing, and erasing operations. The centertap in fact can
be arbitrarily wide. Preferably, the centertap width is a multiple
of the track pitch to facilitate precise track to track movement of
servo and data sensors.
Even though the centertap width can be arbitrarily wide, in
practice it is desirable to have it be as narrow as possible, yet
still meet reliability and fabricability requirements. Generally,
this means that the width of the centertap needs to be greater than
about 4 .mu.m. Preferably, for servo band(s) of uniform servo track
pitch and alternating tracks having respective azimuth angles of
.theta. and -.theta., then the centertap width is given by
wT.sub.s, where w>1 and T.sub.s is the servo track pitch. More
preferably, the centertap width W is increased by the equivalent of
nT.sub.s/cos .theta., where n is an integer equal to 2 or more;
.theta. is the positive value of the azimuth angle (.theta.=0 for
conventional recording) of the servo transitions; and T.sub.s is
the servo track pitch. The servo band width preferably is
correspondingly increased by the increased span of the
centertap.
As another feature that may facilitate use of centertapped servo
heads in the practice of the present invention, although the track
pitch T.sub.s of the servo tracks may be the same as or different
than the track pitch T.sub.d of the data tracks, it is more
preferred that T.sub.s>T.sub.d. Preferably, T.sub.s=mT.sub.d,
where m is an integer greater than 1 and preferably is 2. That is,
the pitch of the servo tracks is wider than the data track pitch
T.sub.d, and preferably is about doubled (2T.sub.d).
As still another feature that may facilitate use of centertapped
servo heads in the practice of the present invention, the widths of
the servo sensors may be increased relative to conventional
practice. This is especially useful to use in combination with
wider servo tracks. Preferably, each sensor in the centertapped
reader has a width in the range from about 1.2T.sub.d/cos to about
2T.sub.d/cos .theta., where .theta. is the positive value of the
azimuth angle and T.sub.d is the corresponding pitch of the data
tracks.
Representative advantages of the increased width servo tracks and
servosensors, e.g., doublewide tracks and sensors are shown in
FIGS. 7a, and 7b. FIG. 7a shows a data recording system 200 of the
present invention comprising servo head 202 and data head 204
engaging magnetic recording tape 206. Servo head 202 includes right
lead 208, left lead 210, wide center tap 212, first sensor 214, and
first sensor 216. Data head 204 includes right lead 218, left lead
220, and sensor 222. Tape 206 includes at least one servo band 224
including a plurality of servo tracks 226a, 226b, 226c, 226d, 226e,
and 226f containing azimuth (zigzag) servo transitions (not shown).
Centertap 212 is wide enough such that sensors 214 and 216 engage
non-adjacent servo tracks 226b and 226f. Note that representative
servo track 226f is characterized by a capture range R that is
about as wide as the servo track pitch. Tape 206 further includes
at least one data group 230 incorporating at least one or more data
bands, one data band 232 being shown. Data band 232 includes data
tracks 234a, 234b, 234c, 234d, 234e, and 234f.
Sensors 214 and 216 have a width that is similar to the width of
servo track 226f. Servo track 226f, in turn, has the same pitch as
the data tracks 234.
Yet, in a situation where the servo sensors are used for tracking
on alternate data tracks, such as in azimuthal recording, the servo
tracks and servo sensors can be increased in width, preferably up
to approximately double the data track width. This allows up to a
doubling of the servo signal amplitude, doubling of the capture
range, and decreased sensitivity to media defects.
Thus, FIG. 7b shows a data recording, playback, and erase system
300 that is similar to system 200 of FIG. 7a, except that wider
sensor, centertap, and servo track features are used in the servo
aspects. Specifically, data recording system 300 of the present
invention comprises servo head 302 and data head 304 engaging
magnetic recording tape 306. Servo head 302 includes right lead
308, left lead 310, wide center tap 312, first sensor 314, and
first sensor 316. These are twice as wide as those of FIG. 7a. Data
head 304 includes right lead 318, left lead 320, and sensor 322.
Tape 306 includes at least one servo band 324 including a plurality
of servo tracks 326a, 326b, 326c, 326d, 326e, and 326f containing
azimuth (zigzag) servo transitions. The pitch of these is double
that of those in FIG. 7a. Centertap 312 is wide enough such that
sensors 314 and 316 engage non-adjacent servo tracks 326b and 326f.
Tape 306 further includes at least one data group incorporating at
least one or more data bands, one data band 332 being shown. Data
band 332 includes data tracks 334a, 334b, 334c, 334d, 334e, and
334f. These have the same pitch as those in FIG. 7a.
Because of azimuth recording in the servo band, the servo sensor
width can be greater than, and preferably up to about double, the
data track pitch, while the optimum servo sensor width is equal at
least to the servo track pitch. Note that representative system 300
is characterized by a capture range C that is about as wide as the
servo track pitch and is much larger than range R in FIG. 7a. As
compared to the servo characteristics of system 200 of FIG. 7a,
system 300 of FIG. 7b will tend to provide a stronger servo signal,
will tend to have a higher signal to noise ratio, and will tend to
be less sensitive to media defects.
FIG. 8 shows one illustrative embodiment of a data recording system
400 incorporating many of the advantageous servo features described
herein. FIG. 8 shows a data recording system 400 of the present
invention comprising centertapped servo head 402 and data head 404
engaging magnetic recording tape 406. Servo head 402 is shown
schematically as including first sensor 408, second sensor 410, and
wide center tap 412. Tape 406 includes at least one servo band 414
including a plurality of servo tracks 416a, 416b, 416c, 416d, 416e,
416f, 416g, 416h, 416i, and 416j containing azimuth (zigzag) servo
transitions. Centertap 412 is wide enough such that sensors 408 and
410 engage non-adjacent servo tracks 416c and 416e. Note that
sensors 408 and 410 are generally canted at an angle in azimuth
fashion so as to be generally parallel to the azimuth angle of the
servo transitions in tracks 416c and 416e. For comparison, a more
conventionally structured centertap servo read head 418 is
schematically shown in the practice of the present invention as
engaging a single azimuth servo track 416g.
Tape 406 includes at least one data group incorporating at least
one or more data bands, one data band 422 being shown. Data band
422 includes data tracks 424a, 424b, 424c, 424d, 424e, 424f, 424g,
424h, 424i, and 424j, wherein data head 404 is shown as engaging
data track 424b. Note that head 404 is generally co-linear with
servo sensors 408 and 410 and also generally is canted at an angle
so as to be generally parallel to the azimuth angle of the data
transitions in track 424b.
FIG. 9 shows another illustrative embodiment of a data recording
system 500 incorporating many of the advantageous servo features
described herein. FIG. 9 shows a data recording system 500 of the
present invention comprising centertapped servo heads 502a and 502b
and data head 504 engaging a portion of a magnetic recording tape
506 (five alternative positions of the heads 502 and 504 are
shown). Servo signals from each of servo heads 502a and 502b are
compared or otherwise coordinated to help guide data head 504
during reading, writing and erasing operations. Servo heads 502a
and 502b are shown schematically as respectively including wide
first sensors 508a and 508b, wide second sensors 510a and 510b, and
wide center taps 512a and 512b. Centertaps 512a and 512b are wide
enough such that sensors 508a, 508b, and also sensors 510a and 510a
engage non-adjacent servo tracks, respectively. Note that sensors
508a, 508b, 510a and 510b are generally canted at an azimuth angle
so as to be generally parallel to the azimuth angle of the servo
transitions being read.
The portion of tape 506 that is shown (unshown portions would
include additional servo bands and data bands) includes at least
two servo bands 514a and 514b including a plurality of servo tracks
516a, 516b, 516c, 516d, 516e, 516f, 516g, 516h, 516i, and 516j
contain (zigzag) servo transitions. The widths T.sub.s of the servo
tracks and each servo sensor 508a, 508b, 510a and 510b are
increased, e.g., wider than the data track pitch T.sub.d,
preferably about doubled (2T.sub.d), and the centertap is widened
in such a manner to allow the servo sensors 508a, 508b, 510a and
510b to span more than one, e.g., several, servo tracks.
Tape 506 includes data group 520 positioned between servo bands
514a and 514b. Data group 520 incorporates at least one or more
data bands, one data band 522 being shown. Data band 522 includes
data tracks 524a, 524b, 524c, 524d, 524e, 524f, 524g, 524h, 524i,
and 524j. Note that head 504 is generally co-linear with servo
sensors 508a, 508b, 510a and 510b and also generally is canted at
an angle so as to be generally parallel to the azimuth angle of the
data transitions in data track 524b.
Note that each servo band 514a and 514b contains ten servo tracks,
wherein the azimuth angle of the servo transitions alternates in
zigzag fashion from track to track. Thus, each band 514a and 514b
contains five alternating servo tracks having servo transitions at
a positive (or negative) azimuth angle and five alternating servo
tracks having servo transitions at a negative (or positive) azimuth
angle. FIG. 9 shows servo heads 502a and 502b in five respective
positions accessing all five of the alternate servo tracks in each
of the servo bands 514a and 514b containing the ten servo tracks.
Likewise, data head 504 thereby is shown in five respective
positions accessing all five of the alternate data tracks in the
data band 522 containing ten data tracks.
The embodiments of the present invention described above generally
include one kind of servo feature (e.g., azimuth servo transitions)
encoded in the servo bands to assist in keeping the servo head(s)
and the corresponding data head(s) on track. The preferred azimuth
servo transitions constitute an amplitude modulated encoding scheme
whereby the amplitude of the detected servo signals indicates
whether the servo head is on track or not. In other embodiments of
the invention, servo bands may include two or more kinds of encoded
features to perform multiple servo functions as desired. In
preferred embodiments, the encoded features may include amplitude
and time based features. For example, the amplitude based encoding
features can be used for on track guidance, and the time based
encoding features can be used for identification purposes, e.g.,
track identification and/or group identification. These different
kinds of features may be encoded into the same or different sectors
along a servo band using one or more servo writing heads comprising
one or more write gaps by which track following features are formed
and one or more writing gaps by which track identity and/or track
group identity features are formed. A representative servo writing
head containing both servo guiding and track ID writing gaps is
described further below.
In some embodiments of the invention, for example, it is proposed
that one or more track identification (ID) sectors would be
interspersed along a servo band. From one perspective, the
resultant servo band could be viewed as containing servo sectors
and ID sectors alternating down the length of a servo band.
Embodiments of the invention including this pattern are discussed
further below. In addition to track identification, such ID sectors
also could provide longitudinal position information during data
seeks. Further, each time any the servo elements encounter one of
the track/group identity transitions, the element may be energized
across its full width. This could provide quasi-continuous
amplitude calibration to correct for any variations in the
individual sensors sensitivity due to manufacture or drift.
Any suitable servo pattern(s) may be written respectively in the
servo sectors or ID sectors of a servo band. The servo sector
portions of the band are preferably written with one kind of
encoding scheme such as, e.g., amplitude encoded zigzag transitions
as described herein, while the ID sectors are encoded with another
scheme, e.g., time-base encoding such as "chevrons," "diamonds,"
"vee or inverted vees," combinations of these, or the like. Such
time-base encoding features per se are known and have been
described, for example, in U.S. Pat. Nos. 5,930,065; 6,021,013; and
6,282,051.
The spacing and length of such ID sectors along the servo band
could vary over a wide range. In theory only two ID sectors would
be required, one being at the start and the other being at the end
of the tape (keeping in mind tape is often bidirectional). However,
in case of loss of position on the tape, it is desirable to include
additional ID sectors along the length of the tape. These ID
sectors could be spaced as close as a few dozen transitions, but
that would not be necessary and would allocate a relatively large
percentage of the servo band to track ID features. Preferably,
spacing of these ID sectors from 25 mm to 250 mm apart would be
adequate. More preferably, these sectors are of such duration as
not to affect the tracking ability of the servo system, e.g., less
than one percent of the servo track length. At an anticipated servo
signal transition density and required sector length, the ID
sectors would take up less than 0.4 percent of the servo band at 25
mm spacing.
The length of an ID sector is not critical, but preferably should
accommodate one or more factors such as being long enough to
include a desired track identity pattern; being short enough so
that the servo signal tracking PLO will not drift off frequency;
being of constant length across all the servo bands; and the like.
ID sectors having a length in the range of 50 .mu.m to 110 .mu.m
would be suitable when using time-base encoding features.
According to one approach, the ID sectors could be created by
holding a track following servo pattern writer (azimuth pattern
writer) in one polarity for the desired sector length, e.g., 50
.mu.m 110 .mu.m. This creates a DC magnetization of the media in
that sector. These ID sectors could then be overwritten by pulse by
a precisely aligned track/group ID writing head having the desired
encoding pattern. This writing would occur at a well-controlled
position within the ID sector, based, for example, on the
servowriter speed and the distance between the zigzag write gap and
the TI gap. This would tend to produce a magnetization in the
media, which is of the opposite polarity to the DC magnetization of
the sector. The servo signal would be coupled with a narrow band
width phase-locked loop, PLO, which could be used to drive the
recording circuitry resulting in "constant density" recording vs.
constant frequency recording. A preferred technique for creating
servo information in a data storage medium is described in
Assignee's co-pending U.S. patent application Ser. No. 10/768,719,
titled Apparatuses and Methods for Pre-Erasing During Manufacture
of Magnetic Tape, naming as at least one inventor Matthew P. Dugas,
filed Jan. 30, 2004, the entirety of which is incorporated herein
by reference.
During or after writing the servo bands, track ID characteristics
may be established. To accomplish this, a servo band is accessed so
that a servo verify read head is phase locked to the first servo
track in that band. Only the first band is required for the track
following of the servo verify head as all the bands and their
signals are instantaneously spatially fixed by the geometry of a
single track wide servowriter head that can be used to create the
servo bands (see FIG. 15 and its related discussion for a
description of such a head). Since each of the servo elements would
engage the same azimuth transitions of the chevron across their
full length, the first transition can be used to calibrate their
amplitudes so any drift in the heads or the channel can be
corrected. Since it would be the same transition for both elements
and the nominal signal from the tape would be the same, the exact
amplitude would not be critical for calibration.
A narrow band width, long time constant phase locked loop is locked
to the constant density, track following servo signal from the
servo verify sensor, and a precise timing pulse is produced at each
clock. The servo channel detects the presence or absence of
transitions in the servo signal from the tape. When it detects a
gap in the track following portion of the signal it counts the
number of clocks between the track following signal and the first
track/group identity transition. This count represents the distance
between the end of the track following portion of the servo signal
and the first track/group identification transition. This count is
then stored and recorded in the work area at the beginning of the
tape. This is done for the first servo track in both directions,
which may be the first transition of each chevron based on the tape
direction.
This count may be taken for all the other tracks in the servo band
or can be calculated based on the azimuth angle of the track/group
identity transitions, servo track width, and the speed of the tape.
Using such information to calculate such distances is feasible due
to precision photolithography techniques that may be used to very
accurately create the writing gap features in a servo writer head
that may be used, in turn, to create the servo transition features
on a data storage medium. Such a head is described further below in
connection with FIG. 15. Preferably, the servo signal density is
high enough to produce a sufficient difference in the pulse count
from adjacent tracks to keep the tracks distinguishable
notwithstanding reasonable tolerances that may later occur. When
the tape is used in a tape drive, the record/reproduce head is
positioned proximal to the first servo track and then locked to it
in the work area where it reads in the pulse count for the first
servo track and the other servo tracks or the servo processor
calculates the other counts. This count is then compared at the
first track/group identification sector and the head moved
appropriately as necessary. Subsequently, this process may be
repeated at each sector. If the tape should be stopped anywhere
along the tape, in short order, the correct servo track can be
reacquired by comparing the distance count with the stored or
calculated value. In other embodiments using a centertapped servo
head, the upper and lower portion of the chevron can be determined
by suitable time base comparison, e.g., comparing the pulse count
difference between the two halves of the servo head.
FIG. 10 illustrates a representative portion of a servo system 600
whose servo band 602 incorporates track following servo sectors 604
and a representative ID sector 606. The track following servo
sectors 604 incorporate servo tracks 608 and 609 in which servo
tracks 608 contain servo transitions 610 written at alternating
azimuth angles relative to tracks 609. Across the width of the
servo band 602, the servo transitions form a zigzag pattern. These
are generally written by pulsing a servo writing head (not shown)
having a zigzag writing gap at an appropriate frequency as the head
moves down the length of the corresponding servo band. ID sector
606 includes opposed "chevron" transitions 614 and 616. The chevron
transitions 614 and 616 preferably are written with a separate,
independent servo writing gap with respect to the writing gap used
to write the azimuth servo transitions 610.
The manner of writing the zigzag servo transitions 608 and 609 and
the chevron features 614 and 616 is shown by pulse plots 630 and
632. Plot 630 shows the pulse of a servo writer head (not shown)
having a zigzag writing gap used to write the zigzag transitions
608 and 609 as a function of position along the length of servo
band 602. Note that the pulses corresponding to the transitions 608
and 609 do not occur within ID sector 606, indicating that the
zigzag transitions are not written in that region. Note that such a
servo writer head having a writing gap corresponding to the zigzag
pattern of the transitions 608 and 609 across the width of the
servo band 602 is pulsed at a generally constant frequency to
create these features in the servo sectors 602. Plot 632 shows the
pulse of a servo writer head (not shown) having chevron style
writing gaps used to write the chevron patterns 614 and 616 as a
function of position along the length of servo band 602. Note that
such a servo writer head having writing gaps corresponding to the
opposed chevron pattern is pulsed once at a desired time to create
the features in ID sector 606. FIG. 15 shows a servo writing head
having writing gaps capable of writing both zigzag transitions 608
and 609 as well as chevron pattern 614 and 616.
A servo reading head 620 includes servo sensor 622. Head 620 is
shown in two positions. Specifically, head 620 is shown in the
track 0 and track 2 positions, respectively, to illustrate the
different time count provided by the time-base encoding features as
between "adjacent" tracks of the same azimuth angle. In FIG. 10,
the tracks 608 may be consecutively denoted with even numbers as
tracks 0, 2, etc., while the tracks 609 written at the opposite
azimuth angle may be odd-numbered, e.g., 1, 3, etc. Note that the
head 620 is generally aligned with the azimuth angle of the servo
tracks 0 and 2 being respectively read in the two positions. Note,
too, how the azimuth angles of the legs 624 of the transitions 614
and 616 match the azimuth angles of one alternating set of the
servo tracks 608, while the azimuth angles of the legs 626 of the
transitions 614 and 616 match the azimuth angles of the other
alternating set of the servo tracks 609.
Transitions 614 and 616 advantageously function as time-base
encoding features that provide track ID information. Specifically,
the time-base servo information read from these features allows
system 600 to actively identify which of the servo tracks 608 and
609 is being read. Typically, numerous track and group identity
sectors are embedded down the length of the tape in each servo band
so that the track identity may be quasi-continuously updated. Track
identity is achieved by tracking the PES with a narrow band phase
locked loop with a long time constant. This provides counting
pulses from the last transition of the track following PES signal
to the first transition of the chevron. During servo writing of the
tape, the pulses are counted by a servo verify head and stored at
the beginning of the tape. The count number then identifies the
track. The distance for each track can be measured and recorded.
Alternatively, using the azimuth angle and the servo track pitch,
such distance can be calculated inasmuch as the locations of the
track/group identity transitions preferably have been established
for all tracks and servo bands by precision photolithography (see
below for the discussion of how the writing gaps corresponding to
the servo and ID sectors are positioned and formed in the
servowriter head shown in FIG. 15).
The track identification functionality is further shown by plots
635, 636, 637, 638, and 639 in FIG. 10. Each of these plots shows
servo information derived from servo band 602 as a function of
position along the length of servo band 602. Plot 635 shows the
servo signal derived by servo reading head 620 as head 620 moves
along track 0. Plot 636 shows the clock ticks corresponding to
clock periods in which a servo transition is detected along track
0. Note that clock ticks 636a and 636b represent clock ticks
corresponding to the azimuth servo transitions in servo sectors
604, while the clock ticks 636c represent clock ticks corresponding
to the chevron style transitions in ID sector 606. Note timing gap
639 between clock ticks 636a and 636c. Plot 637 shows the PLO clock
pulses. Comparing the PLO clock pulses of plot 637 to the detected
pulses in plot 636, it can be seen that there are, in this example,
nine PLO clock pulses associated with timing gap 639. Consequently,
a timing gap characterized by nine PLO clock pulses identifies
track 0. Note that it is not necessary to measure the total length
of the gap (i.e., the length of the ID sector 606) to obtain track
ID information.
Plots 638 and 639 shows similar information obtained with respect
to track 2. In this case, the PLO pulse count associated with the
timing gap 641 for track 2 was 13 pulses, meaning that such a
missing pulse count indicates that track 2 is being read. Hence,
the timing gap offset between track 0 and track 2 is four (4)
pulses. Subsequent alternating tracks would increase by a suitable
count, e.g., a count of 4, for each increasing track number. With
this illustrative four bit or more difference, the count could vary
by .+-.1 without loss of track identification. Of course, the
number of missing pulses used to identify such tracks need not be 9
or 13, but rather the number of missing pulses to be used to
identify a track may be quasi-arbitrary. Preferably, though, the
count is consistent across all the servo bands of the medium being
used for reading, writing, and erasing.
In some modes of practice, it is further desirable that a servo
system provides not just track identification but also group
identification. FIG. 11 shows one embodiment of a data recording
system 650 the invention that provides both track and group
identification. System 650 includes a tape 652 incorporating a
plurality of servo bands 654 and data bands 656 arranged in groups.
Each servo band 654 includes azimuth servo features 656 in servo
sectors 658 for on track guidance as well as opposed chevron
features 660 in ID sectors 662 for track and group identification.
Data sensors 664a, 664b, 664c, and 664d engage the data bands 656,
while servo sensors 666a, 666b, 666c, 666d, and 666e engage the
servo bands 654. Group identification is provided in a manner
similar to that used in LTO drives, i.e., shifting the position of
the chevron transition features 660 in ID sectors 662 so that
timing between the left and right servo sensors would be unique.
This is denoted in FIG. 11 by the different distances x.sub.1,
x.sub.2, and x.sub.3.
FIG. 12 shows another embodiment of a data recording system 680 of
the invention that provides both track and group identification
even with loss of position so that an adjacent track would not be
confused, for example, with trk 0 or 1 in the wrong group. System
680 includes a tape 682 incorporating a plurality of servo bands
684a, 684b, 684c, 684d, and 684e as well as data bands 686a, 686b,
686c, and 686d arranged in groups 0, 1, 2, and 3. Each servo band
684a, 684b, 684d, and 684e includes respective azimuth servo
features 686 in respective servo sectors 688 for on track guidance
as well as respective opposed chevron features 690a, 690b, 690c,
690d, and 690e in ID sectors 692a, 692b, 692c, 692d, and 692e for
track and group identification. Data sensors 694a, 694b, 694c, and
694d engage the data bands 686a, 686b, 686c, and 686d, while servo
sensors 696a, 696b, 696c, 696d, and 696e engage the servo bands
684a, 684b, 684c, 684d, and 684e.
Group identification is offered by the differing chevron patterns
associated with each group. Thus, groups 1 and 2 in FIG. 12 differ
from group 0 in that servo bands 684b and 684d include successively
additional chevron features. Advantageously, this approach allows
the first time base transition in the ID sectors 692a, 692b, 692c,
692d, and 692e to remain the same distance from the beginning of
the sector, preserving the same trk 0, and subsequent tracks,
reference distance. The disadvantage of this approach is that a
servo writing head with many write gaps would be required to create
the time base encoding features.
FIGS. 11 and 12 differentiate ID sectors from one another via
staggered transitions and/or different numbers of transitions.
Other ways of differentiating ID sectors may also be used in the
practice of the present invention. As another illustrative
approach, the spacing among the time base features can be varied.
This may be accomplished by changing the pulse frequency among the
ID sectors as desired for suitable differentiation. As another
approach, the time base features can vary in thickness. These
features can be made by using writing gaps of varying dimensions.
These alternative approaches are shown in FIGS. 13 and 14,
respectively.
FIG. 13 shows one embodiment of a data recording system 700 of the
invention that incorporates two or more encoding schemes for servo
functionality, e.g., at least one or more amplitude-based features
for on track guidance and one or more time-based features for track
and group identification. System 700 includes a tape 702
incorporating a plurality of servo bands 702a, 702b, 702c, 702d,
and 702e and data bands 704 arranged in groups 0, 1 and 2. Each
servo band 702a, 702b, 702c, 702d, and 702e includes azimuth servo
features 706 in servo sectors 708 for on track guidance and further
includes opposed chevron features 710a, 710b, 710c, 710d, and 710e
in ID sectors 712a, 712b, 712c, 712d, and 712e for track and group
identification. Data sensors 714a, 714b, 714c, and 714d engage the
data bands 704, while servo sensors 716a, 716b, 716c, and 716d
engage the servo bands 702a, 702b, 702c, 702d, and 702e. Group
differentiation among the servo bands 702a, 702b, 702c, 702d, and
702e is achieved by the variation in differential spacing among
chevron features 710a, 710b, 710c, 710d, and 710e in groups 0, 1,
and 2. This variation may be achieved in a variety of ways such as
by adjusting the length of the track ID pulse 632 in FIG. 10, or by
varying the width of the track ID writing gaps, or the like.
The above figures illustrate time-based servo transitions provided
as opposed chevrons. Of course, other styles of time-based servo
transitions could also be used in track and group ID sectors.
Representative examples of such other time-based transition
features include any time-based features known in the art,
including, for example, diamond-shaped transitions, vee, inverted
vee features, combinations of these, or the like. For example, FIG.
14 illustrates a servo band 850 comprising servo sectors 852 and an
ID sector 854. The time-based transitions in ID sector 854 are in
the form of an inverted vee 856. The servo sectors incorporate
azimuth style servo transitions 858 and 859. Note how one leg 860
of the inverted vee 856 is parallel to servo transitions 858, while
other leg 862 is generally parallel to servo transitions 859.
To summarize, group identification system preferably is achieved by
varying some characteristic of the time base features among servo
bands in different groups. This is accomplished by providing
differences in the transition characteristics that are unique among
any two groups. The preferred approaches include the following
strategies. First, one approach varies the distance of the
track/group identity transitions from the beginning or end of the
track/group identification sector. Distances to track 0 and
subsequent tracks will vary depending on the group. Another
approach varies the number of track/group identity transitions.
Still another approach varies the down track space between the
track/group identity transitions. This is the most preferred method
because it requires the least number of gaps, and more than one
sector for each data group can be used to independently verify
track identity.
Servo bands incorporating one or more principles of the present
invention may be written using novel servo writer heads comprising
writing gap(s) corresponding to the servo feature(s) to be written.
For example, a servo head useful in the practice of the present
invention may include a zigzag writing gap to write azimuthal
transitions, writing gaps constituting opposed chevrons to write
opposed chevron transitions into ID sectors, combinations of these,
and the like. Novel heads with these write gap features may be
manufactured using techniques described in U.S. Pat. Nos.
6,496,328; 6,269,533; as well as U.S. Published applications
2001/0003862; 2001/0045005; 2002/0171974; and 2003/0039063, all of
which are incorporated by reference herein in their entireties.
Please also refer to co-pending U.S. provisional patent application
Ser. No. 60/469,521, filed May 9, 2003, titled "DUAL AZIMUTH HEAD
CONFIGURATIONS," including as inventor Theodore A. Schwarz, and
also co-pending U.S. provisional patent application Ser. No.
60/469,518, filed May 9, 2003, titled "DUAL MODULE HEAD," including
as inventor Theodore A. Schwarz, both of which are incorporated
herein by reference in their entireties. Please also refer to
copending U.S. patent application Ser. No. 10/793,502, filed Mar.
4, 2004, titled LARGE ANGLE AZIMUTH RECORDING AND HEAD
CONFIGURATIONS, incorporated herein by reference in its
entirety.
A preferred servowriter head structure contains an aligned sandwich
of independent writers for the track following servo and the
track/group identity patterns alternating between layers for the
servo bands and a non-magnetic layer approximately encompassing the
width of the group of data bands forming data groups incorporating
shared interior servo bands. The substructure includes two
independent writers whose gaps are wide and long enough to contain
the track following servo pattern and the track/group
identification patterns, respectively. These two writers are bonded
together or unitarily formed, along with a non-magnetic spacer
between them for isolation, and lapped to form a smooth continuous
surface. A high moment, low coercivity, mechanically hard magnetic
thinfilm is then deposited on the lapped substructure. This film is
etched with the appropriate pattern to form the track following and
track/group identification gaps for recording on the tape. The film
may be broken (etched) above the non-magnetic spacer to enhance
isolation between the track following writing and track/group
identification writing.
A representative embodiment of a servo writer head 900 according to
these criteria is shown in FIG. 15. Head 900 incorporates writing
gaps to create both azimuthal and track ID transitions on a data
storage medium as is shown, for example, in FIGS. 11 15. Head 900
has a composite substructure formed of various layers. As such,
head 900 generally includes sub-pole members 902a and 902b, gap
layers 904a and 904b, pole members 906a and 906b, and a nonmagnetic
sub-gap layer 908 interposed between substrate layers 906a and
906b. A magnetic thin film layer 910 is deposited over the
structure formed by sub-pole members 902a and 902b, sub-gap layers
904a and 904b, sub-pole members 906a and 906b, and isolation layer
908. Preferably, magnetic thin film layer 910 is a material, such
as FeAlN, that has high moment and mechanically hard, low
coercivity characteristics. The composite structure and gap
features of head 900 provide at least two independent recording
head portions. These include servo pattern writer portion 912 and
track ID/group ID writer portion 914. Each of portions 912 and 914
as a practical matter constitutes an individual recording element.
The servo pattern writer portion 912 and the track ID/group ID
writer portion 914 are built on a common wide gap substructure with
two independently energized gaps. At least one leg of each such
recording element would have a wire coil (not shown) wound around
it or a thinfilm coil (not shown) deposited in each of the sub-gaps
904a and 904b, adjacent to the pole members 902a and 902b,
respectively. for energizing the corresponding element function. A
thinfilm coil is more preferred for high track density structures
with many groups.
Optionally, and as shown, magnetic thin film layer 910 is shown
with a break 915 over the nonmagnetic sub-gap layer 908. In
practical effect, this helps reduce cross-talk between the servo
pattern writing portion 912 and the track ID/group ID writer
portion 914 since sometimes both portions could be energized. The
width of the head 900 preferably would encompass the desired tape
width and there would be one identity write gap for each servo
band. As illustrated, magnetic thin film layer 910 includes servo
pattern writing gaps 916 and track and group ID writing gaps 918
positioned in a manner effective to write the desired number of
servo bands at the desired spacing across the width of the tape
during servo writing operations. The servo writing gaps 916 and the
track and group ID writing gaps 918 preferably are simultaneously
etched in the film layer 910 to provide very accurately positioned
gaps for recording on the media.
For purposes of illustration, enough writing gaps 916 and 918 are
provided so as to provide three servo bands 920a, 920b, and 920c
and two data bands 922a and 922b. However, in actual practice a
greater or lesser number of servo bands may be used as desired. The
intervening portions of head 900 corresponding to data bands 922a
and 922b are not shown for purposes of clarity.
Head 900 may be fabricated in a variety of ways. According to one
approach, head 900 may be mechanically assembled from separate
structures. For instance, two servo writer assemblies may be
provided, wherein each includes first and second sub-pole members,
a sub-gap member interposed between the two poles, a magnetically
permeable layer formed over the sub-pole members and sub gap
members, a servo writing gap pattern formed in a portion of the
magnetically permeable layer overlying the associated sub-gap
member, and a coil energizingly coupled to the assembly in a manner
such that a magnetic flux pattern corresponding to the servo
writing gap pattern can be written in a data storage medium. The
two assemblies may then be adhered or otherwise fixed together so
that the two gap patterns 916 and 918 are in a predetermined
spatial relationship with each other on the resultant data storage
media engaging surface of the resultant compound head 900. The two
assemblies preferably may function independently of each other.
Even though head 900 can be fabricated as two independent heads,
head 900 preferably is fabricated as a unitary structure. Thus,
although it is possible to assemble separate structures for the
servo pattern writer function and the track/group ID writer
function, it is more preferred that the write substructures be
first formed and lapped in unitary fashion before the magnetic
layer 910 is formed so as to incorporate the first and second
writing gap patterns 916 and 918. Such a patterned magnetic layer
910 may be formed in a variety of ways. According to one approach,
the layer 910 is deposited and then the writing gap patterns 916
and 918 may be photolithographically patterned, preferably at one
time, for more precise alignment and positioning of the gaps 916
and 918 with respect to each other. Generally, such etching may be
accomplished by forming a patterned mask onto the magnetic layer
910, wherein the patterned mask includes gap features corresponding
to writing gap patterns 916 and 918 and/or feature(s) serving as a
reference from which patterns 916 and 918 can be accurately formed.
The mask may then be used to help form the writing gap patterns 916
and 918 using a suitable etching technique such as dry etching
techniques, wet etching techniques, focused ion beam techniques,
combinations of these, or the like. Focused ion beam techniques for
fabricating magnetic recording heads are described in U.S. Pat.
Nos. 6,269,533 and 6,678,116, both of which are incorporated herein
in their entireties.
Generally, if two separate head structures are first made and then
assembled to form the compound head structure, the resultant
alignment of the two kinds of writing gaps 916 and 918 is limited
by mechanical precision, which may be on the order of a few
micrometers. In contrast, etching the writing gaps on a unitary
structure incorporating both head portions allows the gaps to be
positioned with photolithographic accuracy, which can be a few
tenths of a micrometer or better. Forming the gaps together using
photolithographic techniques recognizes that accurate placement of
the writing gap features on the head is important but less critical
than the relative positioning with respect to each other. This
unitary approach allows for more precise alignment of the writing
gaps 916 and 918 with respect to each other in each servo band.
Track following recording and track/group identity recording may
occur in the same operation because of the accurate spatial lag of
the track/group identity recorder gap relative to the track
following recorder gap.
Servo bands are described above utilizing a track following
sequence of zigzag transitions in servo sectors interspersed with
track identification sectors or blocks. The track identification
sectors are periodically embedded within the servo band as
comprising a uniform DC magnetization in the media with a pattern
(such as one or more chevrons) provided with opposite
magnetization. FIG. 16 above illustrates a servo write head to
provide such a pattern by pulsations at appropriate timing to
create such patterns at desired locations along the servo band.
A methodology of using the track identification sectors with such a
pattern for track/group identification purposes is based upon the
time period between a reading of a last zigzag field according to
the tape direction and a reading of the time-based transition or
pattern field (based upon the pattern portion of similar cant to
the zigzag portions read for a tape direction). That is, the
spatial and thus temporal distance between the appropriate last
zigzag transition of the track following sequence of a block and
the field portion of the pattern can be used to identify the track.
That spatial or temporal information can be stored at the beginning
of the tape as the track identification information.
However, in order to periodically provide such track identification
sectors, precise control is needed to make sure that (depending on
tape speed and consistency thereof), during the writing process,
the pattern-creating, current pulses are also timed to the last
creation of a zigzag for track following. As described above, the
patterns are created by, essentially, an independent servo write
head (see FIG. 16) where chevrons, for example, are created by one
portion of the servo writer head while the zigzags are created by a
different portion of the servo writer head. Although the servo
writer head is shown and described as preferably being of an
integrated design, the ceramic layer functionally creates
independent head portions with each portion having its own gap
(sometimes called subgap) covered by a thin film layer with the
appropriate pattern (zigzag or chevron) provided as the actual
write gaps.
As an alternative to the above described track identification
sectors, it is contemplated to incorporate one or more zigzag
transitions within an ID sector, and preferably between ID sector
transitions (magnetic field pattern portions) such as those that
would be oppositely canted with respect to one another. As an
example, FIG. 16 schematically illustrates a thin film servo write
head 930 as comprising sub-pole members 934a and 934b, sub-gap
member 936, and magnetically permeable layer 932 overlying members
934a, 934b, and 932. Thin film servo write head 930 includes, as an
ID sector gap writing pattern, a single zigzag gap 939 incorporated
between opposite cants 938 that form a single inverted vee. The
legs of zigzag 939 are alternatingly parallel with the opposite
cants 938, respectively. For any given servo band, such an
identification scheme can be developed including any of the
variations described above regarding other embodiments. Only one
gap pattern is shown on head 930, but in actual practice head 930
is likely to include multiple patterns 950 in a plurality of
channels. Pattern 950 may also be used in a compound head such as
head 900 of FIG. 15 in place of or in addition to pattern 918 of
FIG. 15.
As such, track identification can be accomplished based upon the
design and writing of such a combination pattern including zigzags
and a track identification pattern. Data group identification can
also be achieved with this concept in a number of ways. For
example, the whole gap pattern can be written any number of times
within a track identification sector and/or the number of or
frequency of track identification sectors can be varied.
Alternatively, the location of the zigzag 939 relative to the
oppositely canted transition portions 938 can be varied to identify
a data group. As yet another possibility, this concept can be
combined with the concept described above to not only incorporate a
zigzag pattern into the track identification block pattern but also
to utilize the spacing and thus temporal aspect between a last
zigzag pattern of a track following sequence and a transition of
the identification block pattern. That is, both techniques can be
utilized together for track, group, or any other aspect
identification.
An alternative to providing any number of track following sequence
blocks with periodic track identification blocks, with or without
further data group information or encoding, is to write the pattern
containing both the identification transitions and the servo
transitions in a continuous and contiguous sequence along the tape
as the servo band. A significant advantage of this approach would
be the elimination of a portion of a servo writer head, as
described above and shown in FIG. 16, because only one of the
portions would be needed to create repeated patterns based upon
control of current pulsing. There would be no need to selectively
pulse one pattern from another.
FIG. 17 illustrates another embodiment of a thin film servo write
head 940 comprising sub-pole members 944a and 944b, sub-gap member
946, and magnetically permeable layer 942 overlying members 944a,
944b, and 946. Thin film servo write head 940 includes a servo
writing gap pattern that includes a plurality, in this example two,
zigzag patterns 949 centrally located between sides 948 in the form
of a "vee" or "inverted vee". As shown, preferably there are like
numbers of zigzag and identification patterns, but such is not
necessary. For instance, it may be preferable to include more
zigzag patterns 949 than sides 948 to enhance tracking. Only one
gap pattern is shown on head 940, but in actual practice head 940
is likely to include multiple patterns in a plurality of channels.
The pattern may also be used in a compound head such as head 900 of
FIG. 15 in place of or in addition to pattern 918 of FIG. 15.
FIG. 17 shows how any number of complex patterns (each having
zigzag patterns with identification patterns) can be applied with a
single servo write head having but a single subgap. Such
combination patterns can be similar or different with respect to
one another as desired and in accordance with the concepts
described and suggested above. By creating a servo band comprising
a repeated pattern of a combination of track identification
patterns and any number of zigzag patterns, both the track
following aspect can be accomplished (by following the zigzag
patterns), while track identification and possibly group
identification information is encoded along the entire servo track
length. It is contemplated that any number of zigzag patterns can
be combined with any number of identification patterns and that the
zigzags can be incorporated within a central portion of the
identification pattern or to either side, or a combination of
both.
FIG. 18, similarly shows a thin film servo writer head 960
comprising sub-pole members 964a and 964b, sub-gap member 966, and
magnetically permeable layer 962 overlying members 964a, 964b, and
966. Thin film servo write head 960 includes a triple pattern
wherein the zigzag patterns 969 are spaced before, within and after
portions 969 of a vee-shaped identification pattern. Any variation
of these patterns including such suggested positions are
contemplated, whereas any of these patterns can be created by an
appropriately designed thin film servo writer head having the
pattern gap and as controlled by current pulsing. As above, such
patterns with any combinations of zigzags and identification
patterns can be laid down in periodic track and/or group
identification sectors or as a continuous servo band. Only one gap
pattern is shown on head 960, but in actual practice head 960 is
likely to include multiple patterns in a plurality of channels. The
gap pattern may also be used in a compound head such as head 900 of
FIG. 15 in place of or in addition to pattern 918 of FIG. 15.
FIG. 19 schematically shows a portion of an alternative embodiment
of a servo writer head 980 including sub-poles 984a and 984b and
core member 986. Magnetically permeable layer 982 overlies these.
Head 980 has a writing gap pattern including relatively widely
spaced writing gaps 988 and 989. Gaps 988 include legs that form an
inverted vee, while gap 989 is a zigzag with multiple azimuthal
legs.
FIG. 20 shows a servo band 1100 including a servo transition
pattern 1110 that may be written on a data storage medium by
pulsing head 1000 at an appropriate frequency. With sufficient
spacing among gaps 988 and 989 of FIG. 19, multiple inverted vee
transitions 1020 and multiple zigzag transitions 1130 can be formed
in servo band 1110. The resultant pattern is conveniently formed on
a track/group ID sector of servo band 1100 that may if desired be
used in combination with other kinds of servo sectors, such as
track following servo sectors as described above. For purposes of
illustration, six inverted vee transitions 1020 and six zigzag
transitions 1130 are shown, although head 1000 (FIG. 19) may be
pulsed one or more times as desired. One advantage of this multiple
pulsed approach is that the servo signal obtained from transitions
1120 and 1130 can be averaged to obtain a higher signal to noise
ratio than using only one vee transition 1020 and one zigzag
transition 1130. Additionally, the multiple zigzag transitions
further provide track following information.
The skilled worker will recognize that any servo write head
embodiment of the invention may be used not just for writing but
also for reading, e.g., to verify servo features. In some modes of
practice, the same head may be used to both write and read, e.g.,
verify, servo features. Alternatively, one head may be used to
write servo features, while a different head is used for
verification. The head design may be adjusted to favor writing,
reading, or both functions, primarily by adjusting characteristics
of the coil(s) incorporated into the head. To favor writing, a coil
with fewer turns and relatively large current carrying capacity may
be used. For instance, a representative servo head favoring writing
operations may include a coil formed with three to six coils that
are able to carry about 100 milliamps to about 1 amp of current. On
the other hand, to favor reading (e.g., verifying, a coil with more
turns and lower current carrying capacity may be used to develop
more voltage while carrying a smaller current. For instance, a
representative servo head favoring reading (e.g., verifying)
operations may include a coil formed with 20 or more turns, and
often 50 or more turns, that carry less than 100 milliamps of
current. To favor both reading and writing, a coil may include more
turns and be sized to carry more current.
Other embodiments of this invention will be apparent to those
skilled in the art upon consideration of this specification or from
practice of the invention disclosed herein. Various omissions,
modifications, and changes to the principles and embodiments
described herein may be made by one skilled in the art without
departing from the true scope and spirit of the invention which is
indicated by the following claims.
All patents, patent documents, and publications cited herein are
hereby incorporated by reference as if individually
incorporated.
* * * * *